The boat long ago sailed on Mach/Hurd; there are probably better options in microkernel-land. There's Zircon, but Google laid off a bunch of the Fuchsia folks and has been pretty quite lately. QNX is still a thing, but closed source yadda yadda. Best hope there is probably the L4 family (seL4, et. al).

I would not be surprised at all if we end up with radically different OS architectures than the 1970's model we have today.