This is heavily sensationalized. UEFI "secure boot" has never been "secure" if you (the end user) trust vendor or Microsoft signatures. Alongside that, this ""backdoor"" (diagnostic/troubleshooting tool) requires physical access, at which point there are plenty of other things you can do with the same result.
Yes, the impact is theoretically high, but it's the same for all the other vulnerable EFI applications MS and vendors sign willy-nilly. In order to get a properly locked-down secure boot, you need to trust only yourself.
When you trust Microsoft's secure boot keys, all it takes is one signed EFI application with an exploit to make your machine vulnerable to this type of attack.
Another important part is persistence, especially for UEFI malware. The only reason it's so easy is because Windows built-in "factory reset" is so terrible. Fresh installing from a USB drive can easily avoid that.