Maybe it's untenable, counterproductive or simply a bad idea :-)
But has there ever been any attempt to create an abstraction layer in the kernel that does provide a stable ABI? Something that could be used for certain classes of driver?
I don't know the exact rule, but "abstraction layers" for a driver are disallowed. I believe it was AMD or ATI that added a new driver for a device, but they basically just took the code from their proprietary driver, and then put an "abstraction layer" in the middle. That did not make the kernel overlords happy and that version of the code was never merged.
