Ozzfest will more than likely never happen again.
I don't see why Deftones would ever do Mayhem. They aren't really that heavy. I mean they played Lollapollza so they aren't heavy.
Limp Bizkit would be awesome on Uproar as headliner for side stage.
A7X will either headline Uproar or Mayhem. (or be kickass and headline as last band as Warped!)