I think next year is more likely than any other year for Deftones to play Mayhem Fest. Their new record is coming out October 9th (Chino said that on Thursday). They have solid drawing power and pretty much one of the only bands that can co-headline this that hasn't yet. They won't be the last band to play but they are perfect for the 2nd to last slot. Maybe get Rob Zombie to play last, have Deftones 2nd, and Killswitch 3rd on the main stage?
8/9 Summer Slaughter
9/28 Coheed and Cambria