Originally, I was thinking that I'd really like to see a second year of Horse Hall, but now, while that's still the case, the more I think about it, the more I'd really like to see some things from the perspective of the other halls. I'm especially looking forward to seeing more than the little snippets of the Minnie/Kyo conflict, and maybe being able to actually have a direct effect on that whole situation.
It's probably the thing that nagged at me the most during Horse Hall, because it was set up to seem like a really toxic situation, and it killed me that Mary Sue couldn't really do much to help unless she was married (and even then, the effects of your actions occurred offscreen). I got so frustrated with Professor Potsdam and her lack of responsiveness when you try to talk to her, and I felt really bad for Minnie when I saw that she'd taken Kyo back again for the May Day Ball.
So...yeah. I really kind of would like to see a future game where the protagonist could intervene a bit more directly, either as a rival love-interest, or just a concerned friend. Protecting Minnie would be a good thing, but I'd also be really happy if you could become friends with Kyo and convince him to back off before he gets so crazy.
It would also be cool to get to know and learn more about Jacob, Luke, and/or Logan. Guys act a little differently around other guys than they do when there are girls nearby (or so I'm told by my guy friends, lol) and it would be fun to see what they do when they're not running Bingo games, giving you trick candy, or trying to force your roommate to marry them.
Honestly, the more I think about it, the more awesome I think it will be to get two and (maybe, eventually) four or six different views of the same school year. I'd still love to see a sequel year for Horse Hall at some point, but after giving it some thought, I'm way more excited about the possibility of getting into Wolf, Butterfly, Falcon, Snake or Toad Halls. And I can't wait to see what new characters we meet and what familiar folks have new facets revealed.