Plus DKMS isn't a big deal when it comes to open source drivers.
The only thing that matters in terms of kernel would be things like DRM or AGPGART stuff. DRI
and Xorg XAA/EXA drivers have no dependancy on the kernel beyond that.
It's fairly trivial to manage multiple versions of the Intel driver or have compiled a Mesa
tree and DRI stuff outside your distribution-provided stuff.
It's even possible to switch between multiple versions of DRI drivers within the same X
session. It just requires LD_LIBRARY_PATH tricks to point applications at a different path.
It's not that hard at all.
With the 2D drivers you just copy over the *_drv.so file, and keep backups of the originals so
you can go back if it breaks something.
Occasionally you'll run into kernel-level dependancies for a new texture memory management
change or something like that. But for the most part they can be compiled into modules.