Maybe a secret 11th stage for full immobility? I wouldn't mind being able to make one character too fat to move so they just stay in the apartment or your room for easy feeding.
Viewing post in Indulgences Version 0.7 (Jan. 16th Update) comments
The dialogue of a couple of the characters definitely seems like 10 is not the end, but it seems like they're working on fleshing out the other systems before pushing the others past 10.
Edit: besides how I think it'll be from the context, I also personally hope that 10 isn't the end either. I hate when these kind of games skimp out right at the good parts.
Double Edit: there's a previous post from the author talking about 11+ content so that seems like confirmation to me.
Yeah, Hazel specifically says she's stuck in the apartment now with even her description at stage 10 saying as much, but then she goes about her normal business throughout the city. I'm a sucker for immobility so I would advocate adding it in even if it's a one-girl-per-game kind of thing. It could also be used to unlock their rooms for you to freely enter since they're permanently stuck there, and each one would have a different kind of immobility (the one with a giant chest could have breasts so big she can't leave the apartment anymore, for example).