Apparently it was reported that Dave Lombardo said Slayer were coming back for Soundwave at his clinic in Adelaide or something. Blabbermouth is down so I can't look for the link but google it, lots of people are saying the same.
Whatever headlining band is on the metal stage is going to be on at the same time as Faith No More, so if you wanna see them you'd better hope that whoever is announced is not someone you also want to see.