I don't know why this can't be done. Essentially, it would be an enhanced single character mode. For example, you select Mega Man as your first Survival character, then Cut Man and Ice Man. The three would share powerups. When one dies, the remaining skins based on that character will lose their powerups too. This would allow Survival teams based on franchises, like Mario Survival, Zelda Survival, Contra Survival, and the previous mentioned Mega Man Survival. But also allow any combination of skins to be used not just from one character.