I left a comment about a month ago that was this exact idea. But you've worded it way better than what I put. I agree with the personalities becoming too one note after you've had a playthrough with one. I had two quirky personalities in the same town and there really wasn't an incentive to date the second one as the dialogue and interactions was mostly be identical.
This system would really help to make each girl feel their own and create better diversity. I could see the current personalities being the base state for when you meet a girl and it can change through interactions and dialogue choices. Could make the talk options feel important cause once you enter a relationship, it kind of just becomes filler text. Maybe you could give hints or compliment her weight.
To give an example, the base personality for bookish is her love for reading. If she enters the feedee path, she starts reading wg erotica and begins encouraging her and the player to act like in the stories she reads. The opposite would be her sticking to a diet and avoiding overeating through reading health books.
These pathways could be through a major event such as the girl asking if you're intentionally making her fat. With the outcome being based on your dialogue choices and how strong the relationship is. Same would apply for feeder path.
It'll probably take awhile before something like this is in the game, but it could really expand upon the personalities in a great way.
It's a while away yet, but I'd love to include some of these ideas in the 'More Personalities' update.
My original vision for this game was to use procedural generation to create an endlessly replayable weight gain simulator. Probably too ambitious for what I'm actually capable of making, but that's still my aim.
The next update, 'Jobs & Home', will expand more on the jobs and interests held by the girls, which will hopefully add an extra dimension to them so that one Quirky girl is not the same as the next.