I think this might work pretty well for a game without third party. Perhaps third party survivor would work.
I think whenever you start throwing in a 3rd party who can harm both town and scum, then it screws up the balancing. By your table a third party other would require an extra 2 town players/powers, but that harms scum quite significantly. Just look at my game last round, I added in a tracker because of the Gravemind and it just nailed scum's coffin.
So hyped for Rome 2: Total War