Commentators I respect -- over at Patterico's , for example -- characterize this possibility as a "GOP nightmare scenario." For my part, it seems difficult to see many political advantages for Democrats in this idea Klein seems to be floating.
For one thing, it would expose once and for all the cynicism of the identity politics Democrats have deployed against Republicans for so long. The Dems get unprecedented turnout and fundraising in a race with the first serious African-American and the first serious female presidential candidates, so what do they do? Draft a white guy to head the ticket!
Arguments that Obama's black constituency would accept Gore at the head of the ticket but not Clinton strike me as weak. Why should they -- or anyone else, for that matter -- especially if Barack comes in first in popular votes and pledged delegates? He would have earned the nomination fair and square. Yet Klein seems to think it would be just fine for a bunch of Democratic grandees (the superdelegates) to snatch the prize away from an undoubtedly charismatic figure, to bestow it instead on a candidate with limited political skills (as evidenced by his defeat in 2000 after eight years of peace and prosperity) who's so far shown no interest in running. (And notwithstanding all the supposed nostalgia for Al Gore in the country at large, don't forget that John Kerry got 16% more votes than he did.) If all that happened, the young voters who, we're told, have been so "inspired" by Barack will be totally entitled to every shred of their disillusionment.
As for the Clinton partisans, although it's possible that Gore could attract what's often termed Hillary's "Archie Bunker" voters, it's not clear to me that the women who have stood so solidly behind Hillary would be enthusiastic about their candidate being shoved aside so easily. After all, as Bob Beckel points out, she could be the first female vice-president, which isn't nothing. It's not unprecedented for the strong second place finisher to be offered the spot (think Reagan/Bush '80) and Beckel makes some fair points in favor of a Clinton VP candidacy. Ignoring those facts, and knocking her off the ticket to put Gore at the top might well be enough to alienate a significant number of hard core Hillary supporters (like those currently threatening Nancy Pelosi) -- especially if they consider that in the event of an Obama-Clinton ticket losing, she'd be first in line for the top spot four years out.
Gore/Obama may seem like a wonderful dream to Joel Klein, but my guess is that it would turn out to be more of a nightmare for Democrats than for the GOP.