-In my perfect world, NOBODY would give any drivers kernel access.-
That would certainly increase reliability. But I wonder
if such a model would be appropriate for primary storage and video. Some sort of DMA access would still be needed
for these devices to function at acceptable speed.
It's happening all the time, and monolithic/hybrid kernels have to timeslice that anyway. Integrity and QNX are examples in use today in the commercial market. They are also the only kind of operating systems that may be rated EAL7 one day. Windows will never get higher than its current EAL4, and neither will most operating systems, but Integrity is at EAL6+. The seL4 microkernel has even formally verified, and the only operating systems to be evaluated at EAL7 are microkernel-based (it's pretty much impossible for a monolithic kernel to get EAL7).