Its okay to be ambitious as long as you don't bite off more than you can chew. Just like how Nergal is essentially re-releasing the game in increments with new characters, I would recommend doing the same but on an even smaller scale. I can say form personal experience, that if you envision a thing like this as some grand project, it will deter you from trying to take even small steps because of how intimidating the scope of the entire thing is. I would say don't try to create some massive framework recreating the corruption, purity, and neutral routes for all characters at the same time. Personally, I'm most interested in this mod for expanded corruption and dominance paths. What I would do is just expand on the already existing framework by adding and creating more intense domination scenes for each character. Once that's in place you can try to include an overarching story, and then create the alternate paths.
You may already have this in mind, but this is what I would do. I would mod the existing build to allow more for intense domination scenes and give each character its own unique switch/variable to increment the "level counter" for this versions "corruption." From there you include an end game event that triggers once a certain numbers of characters have received max corruption. You wouldn't have to include new areas or assets(at least not yet). Just modify existing dialogue and scenes for more intense dialogue to reflect your intentions. Once you're able to release a build that's able to end the story with each character separately, then go crazy on the joint character interactions, such as what dialogue or scenes are available when just Mom is at max corrupt, or when just Sydney is at max corrupt, or when both are max corrupt at the same time. I'd love to see scenes Mom and Sydney aren't hiding but openly saying what they're doing with him during dinner.
Most importantly though, don't stress about it. You don't owe anything to anyone, so don't work yourself super hard or stress about it. Do what yous wanna do at your own pace. You have my support.