VP9 is not the first proprietary codec, nor is it the first to be offered for free. Industry tends to shy away from uncertain licensing regimes for fear of bait and switch or worse, essential patent holders surfacing later. The MPEG model creates a level of comfort that has obviously worked in the past. And in attendance at MPEG are the best minds in compression and reps from various stored program platforms (other than x86 machines) to ensure wide usability and the best efficiencies. It is doubtful that any one enterprise, even one as well staffed as Google, can muster this sort of expertise and broad agenda. And the feature that is mentioned above is an encoder implementation component that any codec can be built with.
I'm much more interested in seeing widespread support for the upcoming VP9 codec, which depending on when it's released (probably this year) could be even better and more efficient than HEVC.
The Internet will have to switch to a new codec anyway, whether it's HEVC or VP9, and there's no inherent advantage like compatibility or anything like that to HEVC. In fact it may even be easier to convert from h.264 to VP9 for video sites as you can encode for multiple resolutions in the same time I believe, while you can't do that with HEVC.