So what if M$ locks down Surface? The benefits to them are obvious. OTOH, the cast of many other hardware vendors won't just roll over and die either. Their into it to make a profit too. I think for a time Win8/9/whatever may continue to run on third party hardware however these manufacturers want to stay in business simply because it earns a living. If they can't put Windows on their hardware or if they have to compete, they'll find alternatives, such as Android, a Linux distro, or create their own Linux distro, not to forget that there are a few *BSD alternatives out there too. Red Hat, Ubuntu, Mint, and others would love to fill the void.
What about proprietary hardware? GPL can make it difficult however some hardware vendors have distributed binary drivers.As long as the API is documented and the ABI doesn't alter from one Linux release to the next, I'm sure they'll be more than glad to fill that void. I think there may be more opportunity for market share.
The only thing I see that could cause any significant issue to this business model is the coolness factor. If Apple remains the cool gadget to have or if Microsoft shares Apple's coolness, then third party hardware vendors will slowly become extinct and FLOSS as we know it n the desktop, laptop, and tablet will be a thing of the past. It really depends on what the public wants and what they're willing to pay. With BYOD becoming popular,business doesn't have to pay for hardware or software, let the employee provide that.From this POV the bigger fish will eat the smaller fish and we may see the end of FLOSS as we know it.
Ultimately it's hard to say because the fickle public which is usually enamoured with coolness will ultimately decide with their pocketbooks what to spend their money on. If the third party hardware manufacturers can produce cost effective products using FLOSS which have enough coolness to attract the masses, Open Source software will survive. if not, the big fish rule the pond.
P.S. Given the trend of the last 40 years of bigger (the 1%) getting an increasing share of the pie, I feel that over time the world will become a place with fewer choices and more control in the hands of the few. We may not see this immediately but over the next 10-20 years there will be fewer choices.