I have no doubts that it is a good idea. I've been asking for this over and over. We have proof that it woudn't cause any effects on players since Co op Fort came out. I'd like to play with my customized villain, Eddy Raja, Flynn, Lazarevic and all other villains on Co op Arena. It would be awesome and lots of fun. Let's hope for an upcoming patch with this
I still support this, 1000%.
It makes zero sense why this isnt possible(because we all know it is by now) or how it would "break atmosphere" in a wave-survival mode.