This is an amazing thread, thanks!
Would any of you recommend writing/creating a VN that works well enough (interesting story) that the MC can voluntarily skip all potential relationships beyond just friendship/mutual respect/sworn enemies? I.E. any interest in a game where the sex encounters are optional?
There's a fuckton of interest in that, yes. I have one "forced" scene in my game (I say "forced" because lots of people complain that it's forced.... but it's only forced if you choose option A. if you choose option B, then it gets skipped. I guess people's big problem is that there isn't any warning before hand, but tough shit.) and people complain endlessly about it, I've gotten multiple bad reviews specifically because of "forced sex" - literally that was some people's sole reason for leaving a bad review. One guy complimented literally every other aspect of the game, but left me a 1 star review. That was.... I laughed.
Anyway, yea, there's a decent amount of people who want to play "their" way, which means choosing who and what they have sex with - and giving them the option to always say no to everyone, well, lots of people would like that.
HOWEVER. It's only a good idea if it was something you want to do. Problem #1 - doing that, you get a LOT of scope creep, very quickly. Unless it's a very short story, once you get further into the game, it becomes hell on a development side to manage everything properly and have it all make sense. The bigger the game, the more issues you'll have on that front. It eventually means either shorter updates, or much longer update cycles.
Problem #2 - If you set that expectation early, you run the risk of "locking" yourself into it. Locking yourself into anything is NOT something you really want to do if it can be at all avoided. You really want to put yourself in a position to have the creative freedom to make changes, or do things that you might not think of right away but halfway into development you get a great idea and.... oh I can't really do that now, can I? To some extent the story you write locks you in to certain things, but adding additional restrictions on top of that just makes things a lot harder and potentially restricts any sort of creative freedom.
Problem #3 - Related to problem #1 - even if your updates aren't "shorter" they'll most likely be shorter for the player. Any scene you write with an LI that assumes that they hooked up at some point - so you either need to skip that scene entirely for people who DIDN'T make that choice (feels shorter despite same amount of content) or you need to create additional/alternate/etc scenes to work for the situation where they didn't. (longer update times). This would absolutely necessitate additional art (which is the real timesink in all of this) - how you write the scene would determine how much, if you're creative enough you can get away with only a small bit to deal with variances, but sometimes you'll need a lot more than that. It depends.
Problem #4 - It's the type of thing where.... I said there is an audience for it... well not really. It's more like the audience appreciates being able to decide what they do, and when, and with who - but the vast majority of people are totally ok with *eventually* being forced into scenes with characters, as long as they have complete agency over who that's with. The amount of people who would totally be cheering the idea of "it's time to go completely celibate yo!" I feel is probably on the small side.
So while there are plenty of people who would be happy with the choices, the vast majority would also be ok eventually being forced into something, as long as they get to choose the path and aren't forced into multiple characters (outside of harem game sobviously) or something like that. The amount of people you'd actually attract specifically because of this stipulation is pretty small.
It's like most things. If you think about the idea (and all the potential problems that might come with it) and say "Yea I totally wanna do that", then yea there's definitely an audience for it. But if you were doing it just for the audience and it wasn't something you really wanted to do? No it'd be a terrible idea.