The company where I work has recently migrated from Windows XP to Windows 7 as the standard corporate desktop for its entire workforce. Its taken them a long time and a lot of money to do this. I doubt they will be rushing out to buy Windows 8/secure boot hardware for a few years to come. I've also read in the IT press how Windows 8 is likely to flop like Vista. I suspect there's going to be a lot of Windows 7 desktops around for quite some time to come in the corporate world. Which means corporate PC suppliers (HP etc) must sell PCs that can have this feature disabled if they want the corporate business. I am imagining a little switch at the back, turning secure boot on and off, like the little piece of plastic on 3 1/2 inch floppies to toggle the read-only. Worse for the casual user would be a jumper on the motherboard (if motherboards still have jumpers nowadays)
Another question raised in the comments was 'who would step up and manage a key independently of Microsoft'. What about a big PC vendor? They surely have in interest in it, and might get a competitive advantage - as long as its OK to have 2 keys on the same machine, then why wouldn't they? (apart from risking Microsofts ire). They could even charge something for a 'free software key'. I'd be happier paying that, than a Microsoft tax.
That said, the whole scheme is a recipe for abuse by commercial interests. Some entity has to manage the keys, and hence has power over the hardware owner. Power corrupts etc. Who would you trust - Microsoft? HP? Verisign? Your government? Redhat board of directors? Those Debian fanatics? FSF? Pick your poison!