It will def be off Age of Adz, the only question is what song it will be. If I had to guess between two songs I would guess "I Walked" first and "Vesuvius" second. I went to the show in Philly last Wednesday and Sufjan seemed to treat "I Walked" as their single while "Vesuvius" seemed to get the biggest crowd reaction when they first started playing.
he should release "I Walked" as a single, reminds me of Justin Timberlake a little. I could see it doing pretty well.