As someone who played spess for like 3 years and helped sprite a few things, yes the game is a bit of a nightmare to code (I don’t know how to code but I’ve talkes with coders) and can be akward to sprite. That said it is extremely flexible once you can figure things out and there’s several existing databases to pull from. I know vorestation has some very nice descriptions for over eating and vore, though sprites do not have means to reflect this outside of some exceptions.
A suggestion if someone could figure it out would making a more robust paper doll system (currently clothes are overlaid on your base sprite) so you can have body type variants and possibly a higher resolution sprite if you want to get more detailed.
Good luck to any of you who want to undertake this.