So I'm a little late to this amazing thread, but I wanted to throw my two cents in on the Attribute Theft/Transformation part of the game, since that's what I'm most interested in as well. I don't know if you have any kind of interest in muscle growth/height growth, but I think that's a great way to show some of the changing dynamic between Laura and Kate.
You can have it going either way, with Kate trying to push Laura around on something, before realizing she's now eye level with her, and Laura is looking a lot more buff than she remembers...
Or Laura is trying to give orders to the gang about something when Kate challenges her on it, and she has a hard time keeping her composure when she's looking up to Kate's chin and realizing how strong she is.
The last person I'd be interested in how they change would be Dom Hailey. I'd love to see something alongside a bigger dick, like curvier or taller or something, maybe as she gets more confident. Perhaps some kind of progression for her as she goes from being the little sister, to wanting to be the biggest sister, to deciding she's the man of the house now.
I'm sure trying to make all those models would be murder for you though, especially with how much quality you've had in them all so far, but I just wanted to throw ideas out there. Everything looks amazing so far, I'm just excited to see where it all goes.