Even though half the people on this board hate them, I think it would be a good way to mix up the headliners. I'll note a few things that make them a logical fit:
1. With the Cure and Paul Mac headlining, Pearl Jam would be a good, harder "rock" headliner to vary things up.
2. They are reissuing Ten in March, the beginning of a serial set of reissues leading up to their 20 year anniversary in 2011. Pearl Jam doing "Ten" in its entirety would be pretty cool.
3. They have been working on a new album since December with a tentative release of Summer 2009.
4. As everyone has heard, they were supposedly Paul's inspiration for doing Coachella in the first place.
5. Neil Young is conspicuously absent, and there is a mutual lovefest between the two acts - maybe both could be added.
6. The "tour" portion of their webpage is under construction.
7. So, I randomly emailed the official website today asking if PJ was the surprise headliner for Saturday - their response was "we're sorry, but we cannot confirm anything at this time". Doesnt that seem like a strange response?