having had a read of the OGL.org forums it would seem that VBO and PBO are all a part of the super/uber-buffers spec/idea, its just a matter of making sure all the specifics are sorted out so that blocks of memory can be used transparantly for one thing or another and until they have that sorted the driver side of things wont get done, as someone said, you wouldnt like to try to impliment this at a driver level, spend all that time doing it and then find out you have to redo it..
Yeah, I figured they would implement them as part of the buffer object memory management concept. That''s a good idea (yay for standarized interfaces), but look how long it took the ARB members to get VBO done. Granted, there was a whole concept behind this spec (while PBO and uberbuffers would merely be an extension to it), and Microsoft was still on the team happily blocking everything. But still, uber buffers will be a little more involved than, eg, PBO. They need new opcodes / entry points to vertex programs/shaders, in order to access uber buffers at vertex level. Probably some form of ARL, but taking two arguments (or even three, 3D uber-buffers ?). They also need new texture targets, etc.
I''m afraid it will take a while before everybody gives his OK for all this.