I somehow envisioned the game would be played by completion on all stories. I think I would be left unsatisfied if I play with a character only until the nexus and I could not continue the story because I was forced to choose between the two of them.
you can, all you need to do is to pick him....
Much more rewarding would be to be able to play with whoever you want until completion and then choose another and do the same.
again, you can just play the same character until the nexus, and then stick by him until the completion. That way you get one linear story start to finish. If you want to see more complexity, you can save the game just on the nexus, and, once you have done that you can decide to progress the story with that same character or go back, play another one until the nexus and then resume play with the first character..
This will add the complexity of the interactions between the 2 characters (in reality all 4 are there, just 2 with baseline impact and 2 with active player choices).. and that will substantially change the play after nexus with the first character, but you're still playing one character to the end. Then you can go back and pick up the other character from the nexus and see his run play out to the end. It does mean that the post nexus phase is run on individual choices for 1 character whereas the other 3 are locked on what they accomplished in pre-nexus... but that is by design, otherwise we end up with a sandbox that is impossible to manage in terms of who did what first and what the consequences are, expanding the number of possible interactions and couplings by several orders of magnitude.
now, I see your next point
If you want more interconnectivity (this would maybe increase complexity further) you could have nexuses along the way so that what you play with a character influences another character sooner than just ending his path.
For example you have 2 nexuses in a game, so in total 3 stages of the game. Start-1st nexus, 1st-2nd nexus and 2nd-endgame. Whenever you reach a nexus you have the choice to either start with another MC that stage, or continue to the next stage with one of the MCs that reached the current nexus.
For example:
You play all 4 MCs to first nexus. You decide that you only like three of them, so you play with 1st MC to second nexus, 2nd MC to that 2nd nexus and 3rd Mc to that 2nd nexus. Afterwards you continue with 1st MC to finish the story and then maybe also 2nd MC to finish the story, you decide the path for the 3rd MC was not what you wanted and don't choose him anymore.
This is of course only a thought experiment as with the nexuses the complexity grows even more and I don't think this could be implemented without true dedication, not even on paper.
I did think of this, and yes, in a loose format roleplaying game like D&D that's more or less what happens.. but I don't see how that could be programmed and designed and delivered without calling up the NASA and asking for their computers assistance.
Also, you end up on a slippery slope if you place more than 1 nexus and don't alter the gaming experience considerably from one nexus to the next...
what I mean is that if you place 2-3 nexuses in the game and allow the player to jump from one character to the other and do mini-runs and go back every time, the gaming experience between one nexus and the other, is the same as it was before the first nexus, so the player doesn't "see" much of a difference, whereas on the creative side you and up having to add sharks to the hurricane and juggle them both without crashing all over the place.
On top of that, from an end user point of view (which admittedly doesn't really concern me) there will come a demand for even more break points/nexuses in the game.. why have a nexus every.. let's say 2-3 weeks of gameplay, when you could have one every couple of days and customise the game even further?.. slippery slope, as I said.
I am fairly confident that I could create a set of circumstances, scenes, stories and complexities and juggle those in one "interconnective scenario"..and the game could end there.. for personal interest and because that's how my idea came to me in the first place, I can manage prolonguing the game with one main character after the nexus, without further interconnections, but doing more, as I said, exponential growth of stuff to do and things to take into account..
from a narrative point of view also, it would muddy the waters extensively.
from the start there are 4 characters, each with certain penchants, kinks, desires and aspirations.
if you lead them to the nexus, they are well on their way to coming into their own and reaching their objectives despite, or maybe even thanks to the interactions with other MCs or main NPCs... and then you get to see how it all ends.
if after the nexus instead, there is more interconnection and more possibility for "distraction" and deviation of the plot, the narrative loses cohesion because the MC of the day ends up being either still pursuing the same goals and having the same expeiences he had before the first nexus (and then, what's the point of the nexus being there?), or he ends up being all over the place because of a bunch of new variables being introduced, opening and closing new avenues to follow..
which leads us back to sandbox experience. Skyrim is a great game and a great sandbox to explore.. but you end up playing the leader of an assassins guild, the good guy, the hero, the secret thief and tons of other roles that narratively are not compatible with one another. Here you would either have that same problem, or you would have to come up with distinct and individual multiple paths for each MC to explore without every one of them becoming "everything" and doing "everything". There are only so many kinks and situations that you can have your character go through before you get endless repetitions...
so you could decide to not do that..but then, what's the point of a nexus, which ultimately is a turning point?
the concept of the game is the characters are exploring, opening avenues with various NPCs..as they do that, they bump into other MCs and NPCs.. once they reach nexus, the idea is for them to have found their path..the kinks they want to pursue, the girls they want to bed, the harems ors slaves or mistresss they want to play with. in the second part of the game, you get to see them do that.. if you have them again be subjected to further crossings and complications, the characters are either going to loose their way or have a hard time actually reaching those objectives. I'd rather give a single character the spotlight and let him do what he has learned to do pre-nexus and see it come to fruition... even if it means not following the stories of the other MCs (which is only a temporary situation anyway, because you can always go back to your nexus save and run the post nexus with another MC once you've seen how this one ends)
In other words, multiple nexuses equates to sandbox, which complicates the creation of the game, narratively and technically, to a scale I could not begin to fathom, it weakens the concept of pre-and-after nexus, or narrative game (not VN, but still, there's an element of narration and character exploration that has precedence over the jacking off over however many interactions you can manage to reach), and it ultimately weakens the characters, who do have an overarching narrative arch that they should grow into and reach.
As it is, the replay value of the game is already through the roof if you play the game in the spirit it is supposed to be played,.. because you can run 4 characters in any order permutation, and for each of the order permutations tried (and that includes the permutations where you play only 1, 2 or 3 characters), the outcome and the progression would already, ideally, be somewhat altered... and THEN you get to see each main character put his comfy loafers on and reap what he has sown up until then.
Math is not my strong suit but as it is, you get a game that, at nexus point reaches anywhere between 1 and 24 permutations IF you play all 4 characters..
I am not even sure if the number wouldn't increase if you also consider the possibility of playing only 3 out of 4, or only 1, or 2..because those fewer runs would still be accompanied by the baseline values of the other, non played MCs.
Finally, also consider that within each of those MC runs, there are stories that can go in different ways.. so the same permutation can carry over NPCs with different values and "points".
For instance, let's consider the random permutation 2413... that is the order you play the MCs in in this particular playthrough.
what you do with a shared NPC with character nr 2 changes what you can do with it with character nr 1, a little down the line (nr 4 does not share access to that NPC, in this example)... so if character nr 2 makes one choice the NPC has one destiny which character nr 1 can try to alter, another if character 1 leaves it alone.. that same NPC has a different role if character nr 2 makes a different choice, and character nr 1 does something different again (because the starting conditions have changed for character nr 1).
so, within the same permutation of 2413 order of play, you still have multiple variables and multiple possibilities.
say that the NPC in my example is a single girl and character nr 2, the first one to encounter her, makes her his girlfriend... character nr 1 can then turn her into a cheating girl, or work towards an open relationship in which all 3 are equals... or he might just hire her to do his taxes. Either way, this NPC is important enough in both of their lives to merit a role after nexus too...
Likewise, say character nr 2, when he encounters her, acts like a peeping tom and watches her from a distance as she goes about her life or maybe he once helps her out with the rent and has his ways with her.
when character nr 1 encounters her, she's single, and he can still push her towards a NSA open relationship (potentially with character nr 2 if the player decides to play him after nexus), or he can decide to also help her with the rent... or he can instead want her as his girlfriend... or again, hire her to do his taxes.
What you get is, on a single NPC, a bunch of very different scenarios, with a very different vibe to them, despite being able to recycle certain lines of dialogue and thus "scenes".. still within the playthrough iteration 2413, that should be reflected and carry over to after nexus.
and, again, that's just one NPC..then there are the single run NPCs for every MC, and potentially a few more shared ones, either again between character 1 and 2, or between 1 and 3, or 4 (and I am not even going to touch on the possibility of NPCs shared by more than 2 characters).
multiply that level of detail for every one of the 24 or more iterations of the game, and the after nexus paths for each of the MC that results from it, and you get so many possible outcomes that nobody will want for yet another nexus to multiply the outcomes even further.
Simply because the nexus would cause further variations and from 24 permutations pre-nexus, you would get another 24, but each with stats and "experiences accrued" by the various NPCs...
In the case of the NPC contested between MC 1 and 2, every nexus would represent another possibility for that NPC to switch loyalty or destiny.. but it would be come a tug of war that narratively just doesn't work and feels dragged out or pointless.
Yes, you can reduce and restrict things, by leading certain paths for MCs and NPCs to lead to the same destinations/combinations, and recycle content and material from one to the other, but it is already going to look like the inside of a Sarlacc as it is.. no need to add furhter complexity.