You should look into the Mill CPU architecture.[0] Its design should make microkernels much more viable.
* Single 64-bit address space. Caches use virtual addresses.
* Because of that, the TLB is moved after the last level cache, so it's not on the critical path.
* There's instead a PLB (protection lookaside buffer), which can be searched in parallel with cache lookup. (Technically, there's three: two instruction PLBs and one data PLB.)