Most early flash BIOS machines had emergency reflash from a boot floppy, write protect jumpers, etc. All that went away as mass production happened. I'd expect the same to happen here, top of the line boards for workstations and servers will still tend to do the right thing but cheap consumer products won't.
The cheap ones will also stop allowing the user to rekey or disable the secure boot. On the good side there will be exploits aplenty since it will just be security theater to appease the Hollywierd content gods and vendor locks to stop casual Linux use. It is a feature no customer is likely to ask for and no sales will depend on it being effective, so they will make it as cheap as Microsoft will let them qualify for the Windows 8 sticker with.