Yes, this is precisely the idea of the second of the three technologies mentioned (encrypted media extensions) - let HTML5 video interface with a separate opaqu

Yes, this is precisely the idea of the second of the three technologies mentioned (encrypted media extensions) - let HTML5 video interface with a separate opaque binary plugin that implements DRM. Of course such binary plugins will be browser- and OS-specific, so this is going to result in a lot of problems, and goes against the spirit of the web.