That option makes the PSP invisible to the running OS, but no one knows what is left running on the PSP.
My MSI X399 Gaming Pro Carbon AC motherboard had an option to disable the PSP, but it was removed in the latest bios update. The latest one has an option to turn on SVM (Secure Virtual Machine, needed for virtualization). I can either run VMs _or_ have PSP disabled...
Enabling virtualization is pretty simple,
someone could probably write a little EFI app to do it and chainload from there.