I have been thinking what could be doable and different than that FFA we have currently and I am thinking that something like TF2 Saxton Hale mode would be good as it would have an use of those unique characters you added.
The game mode would simply be about Boss fighting big amount of players with standard equipment who would have just one life but could resurrect each other.
At the beginning of the round one random player could become such of a Boss, and after dying or winning another one would take his place. So in one game few players could play as such, and game would end after certain amount of time.
Characters chosen for Bosses would be random, but every could have huge amount of health points, unique abilities, and weapons balanced in a way so that they wont wipe all of the enemy players in few seconds.
I know it will probably never happen but Im curious if anyone would like something like that, as I remember enjoying playing this a lot
Here is an example how it could look like for anyone interested:
