Post formats seem besides the point. It is just one way to think about UI improvements on the posting side of things. Theme developers have been doing the "post format" thing for a decade (only using taxonomies to control styling rather than post formats).

The thing that I like about Tumblr is not the post formats but the simple UI.

I think there is a need for some UI improvements on the posting side of things, but I don't know that post formats are the solution in and of themselves...