But this particular use-case would still play well with DRM as it's implemented today. Netflix on the browser still has DRM, but since the <video> element is standard, it can still be hooked into and decorated.
Sure... but "technically perfectly capable of supporting this kind of extensibility" is not true in my opinion, you'd need quite a few changes to allow this to happen safely. Apple doesn't even want apps to be sideloaded, so that's a stretch :)
But this particular use-case would still play well with DRM as it's implemented today. Netflix on the browser still has DRM, but since the <video> element is standard, it can still be hooked into and decorated.