Already today you can remove the Microsoft keys from most mein board's UEFI and enroll your own. You can perfectly make your own UEFI implementation without Microsoft.
Except that many component manufacturers release their efi capsules signed with Microsoft PKI. So no, you can't fully remove them if you want to verify updates.
While "So no, you can't fully remove them if you want to verify updates" is a valid point, it's also an answer to a different question than the one asked.