According to what I've heard, U2 had investigated jazz fest but quickly ruled it out because the weekends didn't fit into every member's calendar (the last weekend in April and first in May.)
Then there had been a rumor Edge would come by himself and play the first weekend, given that almost everyone from the Grammy jam session is going to appear those dates. But now that is almost certainly not going to happen, although you never know what will transpire in the next six weeks.
So some folks in Nola are viewing Springsteen as an Edge-substitute -- an okay one in my book, but still, wouldn't you rather have the daddy of Music Rising?