The Genre "Jam Band" has become quite vague these days but there are always some on the line-up every year. You could even make an argument that Grace Potter and the Nocturnals is a Jam Band and they had a great set last year. You'll probably discover a new band you have never heard that could qualify as a "Jam Band" in 2013. As far as the Big Name Jam Bands like Phish, Widespread Panic and The String Cheese Incident, 50 minutes doesn't quite cut it for them unless they are planning on playing one or two songs only and they probably wouldn't be welcomed enough to rationalize their cost as a headliner. Acts like The Disco biscuits and Bela Fleck would be more realistic for the Coachella Line up. With that being said, I would absolutely Love to see any of the following that could possibly be qualified as a Jam Band: Neil Young, The Allman Brothers Band, The Mars Volta or anything Les Claypool at Coachella.