Survival is pretty much Campaign just in higher waves. If you've done the monster fests you'll know and see what I mean.
If anything they should add a new gamemode which caps at around wave 12 but introduces NM+ level mobs. wave 1-5 purple mobs, 6-10 gold mobs, 11-12 some new higher level or nonstop gold ogre/djinn rushes while still keeping the current mob count and have the drops be similar to the appropriate wave 20+ drops. That would probably be hard enough for people while still helping speed up the process into endgame.