Not to be a nag here, but nothing about this (or anything else, for that matter) sounds like Canonical is working with MS on anything...
Not only was this proposal not officially endorsed by anyone working for Canonical (it looks like a community developer brought it up) but MS itself is moving away from silverlight, as far as I can tell. And so is Netflix, eventually. They stand to gain nothing from this, or anything else Canonical is working on.
And the browser plugin is probably not going to make it into the LTS, or maybe even at all into Ubuntu if the dependencies don't get worked out.
Steam is an external application that RUNS under a distro, only SteamOS is a distro itself-and that is based on Debian with Steam installed. Since Steam was willing to create a package that can be run on unmodified distros, that means no distro had to add DRM suppport to get them to write a Linux version. Thus, all DRM support is confined to the Steam code itself, and no attempt can be made to block pulling sound or video off the bus, etc (no protected media paths). The only thing Hollywood-style DRM would offer Steam would be the power to prevent videos from being made of their games being played, so probably they were not even interested in that level of DRM.
A game is not like a movie, where a copy from the audio and video streams is a functional copy of the original work, thus no advantage to sabotaging the underlying OS. Steam seems to be like Pipelight, not like DRM modules for the browser, in this sense: all DRM code is confined to the DRM'ed application. I don't install Steam as I do not play paid games, but the packages I DO install have not been modified Windows-style to support DRM in an effort to attract Steam. Not only that, what DID have to happen was that graphics drivers had to improve, thus causing Steam to in a sense subsidize open-source gaming and 3d content creation.