Well, perhaps the vendors will be releasing something like `legacy drivers' in the future? Say every once in a while they release a driver that includes the ARB_compatibility extension, but their newest lean and mean driver won't contain it (like they do for old graphics cards, every once in a while a new legacy driver is released for old graphics cards, but the mainline drivers don't have support for them). My guess is that the old code won't need every newest driver anyway.
I think that could be a perfect way to phase out the pre-GL3 code and focus on an OpenGL 3.1 driver that is clean.
Personally I'm quite happy with the 3.1 release, I didn't expect the deprecated stuff really to be removed from this release. The uniform buffer is also quite a nice feature. Besides that: 9 months after the previous release, who would have expected that after what happened with OpenGL 3.0?
My guess (hugely based on hope) is that we will see an OpenGL 4.0 version that will be the new rewritten API sooner than most expect. The OpenGL 3.x line is needed for transistion to a new API. They just couldn't make that huge step at once.
Here is a nice blogpost written by Paul Martz on the topic: