From a historical perspective, it just seems inevitable. With Pearl Jam literally introducing Indio and the Polo Grounds to live music in 1993, it can (and has been argued) that without that show, Coachella may not even exist. They had the balls to stage the first ever rock concert on the Polo Grounds and managed to draw 25,000 fans, in the process proving that Indio is a viable place to host live music.
From GV's side, they'd be a major draw. The have one of the most devoted fan bases in the world and have no problem selling out large venues like Madison Square Garden or the Philly Spectrum (for multiple consecutive shows, at that). If they play, you know a large contingent of their fan base would show up. And they are one of the most respected live bands in the world, both by other artists and by knowledgeable observers. It's no stretch to see them as a Saturday headliner on par with Radiohead, Roger Waters, etc.
So...2013 will be the 20 year anniversary of the concert that started it all. On top of that, the band is rumored to be working on their next album, with a release of late 2012 or early 2013 a reasonable expectation. And, they are starting to pick up their touring schedule, with a number of festivals already on the horizon. That doesn't add up to a sure thing, of course, but even at this far-away stage I think it makes for pretty interesting speculation.