The only way they could be on ozzfest would be as either the co-headline for second stage for the first half of the tour and be replaced by someone else (sorta like maiden did this year...) but i doubt that would happen, so the best bet would be ozzfest '07, after they get another album out (another one that gets too much airtime on mtv, of course...) but at least it's something to look forward too. and by then they'll have to take a spot on main stage, maybe slayer's spot from 2004 (the one right below co-headline...about a 45 minute set, which is way too short for them)
Anyway i think that they're going to do another North American tour (at the earliest) in mid-spring, after they take a while off and then get back to touring japan and europe.