A redemption story, yes I've heard/read several people calling for Teh Snah to have his redemption. What would you want for the villain?
Oh I haven't thought about anything substantial, but simply having the sequel perchance continue with its theme on forgiveness, righting past mistakes and understandings (which the first movie quite heavily focused on) in some capacity when it comes to Hans would be something I could appreciate to be explored, especially for someone who tried to commit something heinous.
Since Frozen largely focused on correcting ones "unintentional mistake", it would be interesting to see what Disney would do for someone who deliberately tried to do something wrong and whether such a person would be allowed to be forgiven at all. Always nice method to teach kids about life lessons, and could serve for some nice character development for the guy.