Somehow, I think that in four years voters are going to be asking "John F'in Who???"
Especially if the Swiftees can complete their mission!
I'm no Nostradamus, but I'd place good money that you're right. The only reason why Kerry is supposedly polling so high (of now) is because the campaign just ended and his widespread name recognition. There's bound to be a good number of folks that are still "jazzed up" about him--but that'll fade shortly as they seriously shift their sights to Hillary or if not her, some fresh, more appealing democratic faces (both literally and figuratively!).
Lest we forget, there was the same kind of buzz about Gore right after the 2000 election, many probably thought he would (or at least would stand a good chance of) be the dem nominee in 2004. I'm sure he even gave it serious thought, but one of the big reasons he didn't run is because he knew he wouldn't be able to just walk into the nomination a 2nd time (and hell, it'd be a huge embarassment if he didn't win it). He probably knew it'd be a dogfight, and if Kerry decides to run again, it'll be even more difficult for him to win the nomination among a slate of democrats who'll find that OPEN seat too tantalizing to not give it a shot.