Mystery Band at Ozzfest this year

So anyone have any ideas of it could be? In case you don't know, System of a Down, Disturbed, Hatebreed, and Lacuna Coil will be headlining the main stage at Ozzfest this year, along with a mystery band that will be announced on the 23rd of May. Ozzy will be playing to, but only like 10 shows, which sucks cuz he skipped out on Ohio last year as well. I mean I could honestly care less if he came, but I really wanted to hear him play Diary of a Madman, which is my favorite song by him. Mainly just wondering who the unnanounced band will be. I was hoping Tool, but they have tours in Europe going on at the time of Ozzfest. The only other people I can think of would be Godsmack, Mudvayne, or maybe Korn. Godsmack and Mudvayne would be pretty cool to see. Any thoughts on this?