Do we have more hardware isolation? There was a pretty strong argument against microkernels - a driver running in userspace can still bork the whole machine if the hardware being controlled can write to memory at arbitrary addresses.
On the other hand, datacenters have become so large that a 1% performance improvement can amount to millions of dollars in hardware and energy savings, so the extra cost of a microkernel might not be very welcome outside consumer devices.
Microkernels have won, even if monolitich kernel advocates haven't yet got the message.
they are seldom implemented correctly on firmware/mainboard level.