He's in the cat-bird seat. He'll have his chairmanship and will be courted by both sides. He's not a Republican (he claims he's a John Kennedy Democrat), there's no benefit to him in him changing parties.
It's just the political talking heads throwing up "what if's" to try to seem relevant.
What I think is more likely to happen is that a few nominal Republicans will strongly consider switching parties, especially since the right wing of the GOP seems to think that they lost because they [link|http://www.washingtonpost.com/wp-dyn/content/article/2006/11/11/AR2006111101103_pf.html|weren't right-wing enough].
As far as Lieberman having more power than he would have had as VP, well [link|http://www.suite101.com/article.cfm/presidents_and_first_ladies/35366/3|that's not saying much]. :-)
Cheers,
Scott.