I'm sure we've all been in games where the 3 alliances have poor member distribution at the start. Say, alliance A has no healers while alliance B has 6. Or Alliance C only has 1 person in it because the other 7 were AFK when the duty popped. Perhaps one alliance has no members with a useful limit break.
I think it would be good in these kind of situations if, before the game starts, you could request to swap members between alliances.
I think it could work by nominating yourself to switch to alliance A/B/C (and if that alliance is already full, one of their players would have to nominate himself to switch the other way), and the switch would depend on a majority of players voting to accept it.