I really love it if the option to trade in Ultimate powers for a team up hero was added to the game. Even if it's like some of the other exchange options where it is 3 of one item for 1 of whatever. I would be happy with that. A random costume or one you could pick out by again trading in 3 ultimate upgrades for a costume.
This would really help people like me who are long time players with a lot of unused ultimate upgrades as some characters you just don't care about there ultimates being higher. (Most of the time this happens with players just just not fond off and it seems I always get the freakin upgrade to the ultimate powers for players I'm just not that interested in.)
I just think this would be a great addition to the game. Not sure if they will ever add this, but once can hope :)