Rumor: Slipknot on Graspop 2009?

Yesterday, I was at the Slipknot concert in Antwerp, and Slipknot frontman, Corey Taylor, mentioned (what I think) is a big hint on their possible appearance on Graspop 2009:

You can expect to see us back sooner than you think!

I don't think they'll do new European tour again so quickly after this one (which ends tonight). This opens the door for them to do a string of summer festival appearances. I'm betting Graspop 2009 is going to be on that list!