Well, as I already said in like 3 other threads, I think it would be cool to have a team Mercenary.
They would basically have a rainbow Vault.
Basically, every team, once per round, can decide to take a card penalty (6-12 cards I guess) and hire a mercenary to fight one of their battles. If the merc wins the battle, then he gets to salvage cards instead of the team that hired them, and if the merc loses, then Team Mercenary discards instead of the hiring team, and the winning team salvages cards that Team Mercenary used.
Team Mercenary will be composed entirely of people who were not bidded on, like Underworld.
The team's deckbuilding rules will only be based on ONE player at a time.
So, one member of team mercenary takes cards out of the Vault, then after his battle, puts them back in again, or discards them.
Deckbuilding rules will be the same as Underworld.
Team Mercenary would be good because it offers people who did not have a chance to join a war team the ability to participate in War without necessarily actively competing. This is the main upside to this, they could easily be team rainbow in War #3.
It would also lessen the rate at which "Suicide Decks" Pop up, as the team could elect to hire a mercenary instead.