The formal bikeshedding first: It says earlier in the spec:
"$BOOT/loader/ is the directory containing all files defined by this specification"
The current path to unified kernel images $BOOT/EFI/Linux violates this.

I don't know where/when/if this addition has been discussed, please point me to any discussion. If there wasn't any we should have it now, I guess.

That the path doesn't match is also a hint that it doesn't belong into this spec. I guess it could be handled in an EFI addendum, though?

Also, the spec seems to try to be OS independent on one end. I guess it should try to be architecture/platform/firmware independent on the other end, too.