Gotta ask is it necessary? Those contents are minority and doesn't add anything at all to the main plot. Just increase the pacing for the development and means less contents for people who doesn't like them. Why not add Ntr at this point and say it avoidable. It not happening if you choose to and there are choices to avoid it. Nobody cares if it avoidable or not, they care about how long it will take to finish the game and how much play time will any of us get. You might be fine with playing games that get abandoned or in work for 4/5 years with little to no amounts of contents every 3/4 months but most aren't. Sure, it pretty selfish but those people who enjoy sharing/swinging. Are they okay with less amounts of contents? Like in most heavy based sharing/swinging games there is hardly any Harem or MC fucking his girls lol. (Adventure couples). Most would prefer to watch scenes developing the main li or side li. I don't why it so hard for people to understand that certain kinks doesn't work together. (Proof- Literally half of the abandoned tags games).
They do add something to the plot. It's not about the girls, it's about having male friends who are up to your standards and not some token cucks/nerds/idiots who exist solely for the MC to make fun off and crash under his boot. It makes suspension of disbelief possible. Samir brings value to the story and personally I got a laugh out of Maria shoving a bottle up his ass for fucking up, or Debbie, MC and Monica calling him a pussy to goad him.
You have to understand a few things about preferences. People will whine for everything. They will whine because there is MMF content, they will whine because the dev made it so you can't get Debby without Lisa, or that there isn't enough content with their favorite waifu. They will whine because the son/mother incest is too slow, the girls are too distant, the MC is a naive boy in a world of political intrigue. You can't pinpoint a single thing and claim that this is the end all be all thing that destroys the game, unless it's a technical issue. And when I say "whine", I don't want to offend, but as you understand, there is a sense of entitlement here. I understand the notion of "I like this game so much that it pains me if it goes down a road that I think will cause it's downfall", but there's also the.. other thing.
The best thing we can do as a community when we like the game is protect the developer's vision. If the dev has shown good things and the reception is at the very least fair, he will continue to do so and maybe take our opinions into account. If he gets extremely intense feedback for the small things, he will get bitter and perhaps confused. You don't want that. So as I said earlier, be reasonable.
There exist succesful games which allow the protagonist to help his "bro" get the girl or set MMFs/Swinging as a kink.
Sisterly Lust (completed) allows you to help your friend fuck his sister and talk about it.
Dreams of Desire (completed) allow you to help your friend him fuck his mother and it has MMF content
Anomalous Dr. Vibes allows you to choose a sharing option (although I don't know to what effect, been a while since I played it).
Midlife Crisis also does the sharing/swinging thing and adds a trans character.
There are a lot of other games where you get the choice of not pursuing a girl because she gels better with someone else important to the story.
Additionally since you are talking about development time, have you seen all those slow burns that waste 3/4s of the game on "getting to know you/I'm not ready yet" handjobs and titjobs. Yes, a slowburn progression can be great, especially when accompanied with good dialogue, but you know what I'm talking about. This game has a completely different romance progression where MC tries to make the girls addicted to him by sending them to heaven, something that I really appreciate, because it's a more mature and realistic approach.
You know, I could go on and on why there is nothing wrong with the more fringe fetishes in this game, if they can be characterized as such in the first place, but I think I'll stop now. Perhaps you are on to something with the development time idea, but try to keep things in proportion. For a game which has a lot of sexual content, 2-3 fringe scenes are a small percentage and they have a reason for being there.