well, to be honest, if i get a lot of bad reviews in the first 2 or 3 versions i could stop, i prefer to stop than ruining the story.
Well i'm guessing if NTR was winning a poll in discord you already essentially got a few of those in the form of "I'm out if it 's in. Immediate uninstall!" threats before you even started
Here is thing with that though. What ends up "ruining the story" in a long dead and abandoned game is going to be a subjective value either way. Like take the guy who wrote out the big "respecting the game" speech here. Now take a peek at his post history, and note the very extensive amount of spread out "I don't want NTR in my games" themed comments in there. He doesn't actually gives a flying crap about some need to "respectfully" follow/continue the original script to a T. He's just pushing his own personal likes/dislikes in a veiled manner. Throw some mother daughter incest lesbian scenes or just with you threesomes that wasn't previously in the game either and I'm guessing he'll be perfectly ok with that deviation.
My overall point there being don't get too caught up in the blown way out of proportion perception that the overly vocal against something posters like that and their indirect bullying here would actually make or break you efforts. They don't and never do. MSN succeed because it was very well written game, with girl models that were of the safe bet variety to be universally appealing (bonus points for being that and unique), had a relatable non-kid creepster MC, and above all else had an adequate amount of good quality/hot animated sex scenes paced in for people to jerk off to. Do *ALL* of those elements well enough in a combined package and at that point it doesn't matter if the game has other people fucking in it or not...it'll find that larger scale audience/support.
Like i said earlier though, above all else whatever you decide needs to be a direction *you* are passionate about though. Since it's your own effort level that will be the make or break factor in this attempt. But again I'll point out and from my own personal perspective, if you are looking to dump more effort into this then just putting a bow on the story i don't see sticking to a continuation of the vanilla love story being a winning formula here for you. I mean there is a reason the standard romcom movie isn't seeing the couple cement their relationship half way through and then putting a huge second half emphasize on portraying what the happily ever after looks like. Or take a 5 star quality game like melody or DMD people can find themselves engrossed in - if you start a full evaluation from the point after the mountain was conquered would all those 5 star reviewers still feel the same way about it from that point on? Because that is what you'd be starting from here, minus most of the built from the beginning support behind it. I know i didn't, and doubt I was the only one that found myself eventually spam clicking through even the continuation of different (but similar) sex scenes in Melody just to finally finish it after absolutely loving the first lengthy half of the game.
At that point your invested effort would be better off making a fresh spin off setting game using the same characters. Just my 2 cents though