Even if they are startlingly worse (motoblur seems pretty universally hated, and Sense seems to strongly polarize, some people find it very nice, others find it awful and full of useless gradients and badly polished looks), I doubt they're going to drop them.

And this is terrible for Android as a platform, in my opinion worse than the issue of hardware fragmentation and maybe even worse than the handsets left in the dust re. OS updates, because it means UI knowledge becomes non-portable from one Android handset to the next, which is horrible.