Besides finishing the missing parts of the current characters, I'd really like for them to start working on an endgame. Right now, it is easier to get them to walk around completely naked before you can really afford to buy their outfits. I'd just like some additional interactions that are unlocked at triple 1000 for multiple girls.
Additionally, to be able to afford things faster, I'd like the ability to specify a girl or two as 'workers' and have them bring in more money for you. Pimp them out, as it were. Even if this option was ONLY available for Jean, it would still be worth it. I also like the way the game is set up that your first two girlfriends are your alpha ladies. When you choose who you want brought into the harem, they are the ones to discuss it with you. Perhaps they could work in some scenes having them lord their position over the other girls of your harem.
Have them work in some of the super powers into the sex. Jean gave me the option of a telekinetic handy, but I made her use her real hand simply because she didn't really want to. Also, I didn't trust her to use her powers around me. But there are other girls that aren't taking advantage of their powers. Have Kitty give you a handjob WHILE you are fucking one of the other girls. Make it so that every time you have sex with Laura, you have to pop her cherry. Have a quest you can do to clear that if you can fuck her long enough or something. Have Rogue steal someone's powers to do something really naughty... or something. I don't know.