If he either retires in 2002 or survives the rough 2002 cycle and wins reelection, he'd be a contender for the 2004 Democratic nomination, which might butterfly away a notable supporter's speaking slot at the 2004 DNC:
That being said, it's still plausible Obama, who was clearly going to be elected at that point in his senate race, would get the keynote since the Democrats were looking to build their bench.