triaxial Galaxy?

At morning coffee at OCIW, David Law (UCLA) told us that he has evidence—from the morphology of the Sagittarius stream, mainly—that the Milky Way halo could be triaxial. This is pretty intriguing, because it is the generic prediction for dark-matter halos, as I understand is (substructure notwithstanding). He reminded me of the paradox that the Sagittarius stream must—in any model—be very old, which goes against the idea that galaxies are generically building up their mass through mergers.