If an extension to XvMC or the proprietary ATI/Nvidea equivalent supported a protected path for media content, which could theoretically bypass the kernel by sending ciphertext directly to the renderer, then Widevine or another DRM system could be supported on GNU/Linux.
Seems possible, though theoretical. I would not expect to see this unless somebody was paying for it (no particular reason for ATI/Nvidia/Whoever to go out of their way to support such a thing), meaning that I will not expect to ever see it in "normal" Linux distros (perhaps in "ChromeOS style" locked down distros being marketed with their own completely separate branding).
Proprietary graphics stuff in Linux has always been a world of hurt anyway (despite the lower performance it was a godsend when progress on the radeon drivers started to accelerate). I would expect few Linux users to be thrilled about compromising their streamlined modern Linux installation to watch netflix when a separate Roku or smartphone would do. (I know I would never go for this proposal. It would not be worth the grief to be plunged back into 2005. Not on the computer that I try to get work done on...)
This was the spoken about way of achieving the goal on the HTML WG mailing list, if that is required, on Linux (note Flash doesn't do that currently and many are happy to licence content for it despite that, so this may well never come to fruition).
