I suppose it comes down to the hardware manufacturers really. They could choose to use locked-down BIOSes which would make it impossible to boot anything other than Windows 8, and I expect there will be some who decide to do just that. The only way round this would be to upgrade the BIOS, and this is probably a bit too geeky for most people. But I've no doubt that the inventive Linux people will find ways.
Naturally I'm in full agreement with your last paragraph.