Necro IV in epic is so much fun to hunt slayers because of the high mob density...I'd really like to see the design philosophy going in that direction for future WZs. And I don't think anyone, by L20, is going to have a problem even with that many mobs tuned to Normal difficulty, so it shouldn't be a balance issue.

Whenever the final pass is made for Keep, I hope the spawns are tuned up like that.