As someone who recently had to debug obscure uefi boot issues in embedded systems, I think this is an excellent idea and will result in more secure and smaller boot code.
You think dragging in millions of lines of Linux will result in "more secure and smaller boot code"? Vendor firmware is often crappy, but let's not pretend Linux is smaller.
For which platform? It is really hard to boot an x86 board without using a commercial UEFI.