Not sure if you’ve checked out my topic but my recommendation list has a couple VN sections and it lists fetishes and (last known) development status all related to weight gain. Couple be something on there to check out. I know you are working on a few potential VN ideas not sure what specifically might give you what you are looking for.
Probably won’t be quite what you want but outside of what is on my list there are a few non weight gain VN’s that I’m a big fan of and have some great characters, setups, fetish content and stories. @expandinguniversegame’s Endowed (harem, BE, lactation, preg, in development) probably has like my favorite opening of any VN I’ve played. EUG’s writing feels really natural in a lot of situations the I think the intro and opening of the game is well crafted. And goes to show you can world build and set up characters in an interesting way that has a nice build up before the fetish shenanigans happen. As well as Hypnosis (BE, AE, harem, preg, lactation, in development) the first game by EUG. The dialogue and character interactions in these games are really solid in my opinion. It feels very “human” and each character distinct and different from one another. Which I think is quite the accomplishment with how many girls there are. With branching story paths and multiple endings currently up to 15 chapters (on patreon) the game has a lot of good interactions mixed with good fetish content.
Neokama game’s White Russian(BE, AE, harem, lactation, in development) has some great characters and good interactions set around an bit of a bumbling boob-fiend of an MC. I think this is another good example of how to make girls in a harem situation feel different and unique from one another while equally appealing for their strengths and flaws.
I find myself coming back to these for the characters, story, and fetish content even though they focus on BE rather then WG. Hope something here might be helpful to you, good luck in finding some inspiration to draw from.