Muse- with a new album coming out I would definitely put them atop the list of potential headliners (its not like 3 years is that soon, and this time they'd close out the night, without tiesto closing behind them.)
Depeche Mode- I would killll to see them but I'm curious about the rumor that they didn't enjoy headlining 7 years back. Can someone site the source?
Pearl Jam- I like the 20 years coming home to polo fields idea
I'd put money on 2/3 subheadliners being 2 of the 6: phoenix, jack white, the Weeknd, Beck, MIA, or Sigur Ros.
I also wouldn't rule out Bon Iver headlining. If they come out with another album within the year, they would be the black keys for 2013.