"the competition within the DPJ for who gets to be PM under the Buggin's turn principle"

It certainly looks that way, doesn't it, Earl, when Maehara decides to step up and immediately becomes the favorite.

I think that the LDP habatsu used to help its members with money and appointments and individual elections and the members in return would support their leaders' political progress, hopefully culminating in the prime minister's office. This became less the case near the end of the 1955 regime. There must be oodles of papers and books written on this point alone, so I won't go into the why and how; suffice to say that from that perspective, the Ozawa and Hatoyama groups in many respects look a lot like old-school habatsu. Maehara and Noda are also founders of their respective groups, and Tarudoko and the other Ozawa, two men with obvious aspirations, are also in the process of putting together support groups of their own. The factions/groups in the two parties seem to be going in different directions.

So how far along the path to full-blown classical habatsuhood are the DPJ groups? Dunno, but it looks like something that a PhD candidate can sink his/her teeth into. For starters, I'd look at the MIAC records of the political financing organizations of the DPJ and its Diet members. I suspect that there's not much of a money trail there other than the mysterious Ozawa ATM and the Hatoyama Mama money.