You're literally describing something like macOS/iOS which is based around a microkernel (XNU, based on Mach). See also QNX for a non-unix OS that does this.
Err.. loading drivers dynamically according to a stable ABI doesn't make an OS a microkernel. If the drivers all share the same address space that's a pretty conventional OS. For a microkernel you need to have separate processes for each driver. It's more robust but there's more IPC overhead.