From looking at the spec, all it appears to be doing is creating a protocol for the negotiation of third party platform specific DRM plugins. So basically, platform specific third party browser plugins, but now in the standard for some reason. Why is this necessary? It doesn't make it so that the plugins are platform agnostic or open, it just makes it so that the protocol to load and activate platform SPECIFIC, purpose SPECIFIC, binary plugins are part of the standard now... for some reason. This just makes it more complicated and doesn't actually have any upside!
These closed, binary DRM plugins will still need to be installed, just like flash or silverlight is, and they'll still only be on the platforms that the movie industry considers trustworthy, nothing will have changed except now we have a more complicated spec to follow in order to make a "compliant" browser.