Microsoft video streaming technology over HTTP works just fine and is still fully supported and improved upon, last I checked. It's one of the 4 major implementation of Adaptive Bitrate Streaming (Apple HLS, MPEG DASH, Adobe Zeri and Microsoft Smooth/HDS). The Silverlight requirement was there because the client needs logic to switch up (or down) in bitrate depending on network conditions - instead of buffering, hence the "adaptive" part. The specification is open and anybody can implement it. The DRM part is optional, it's not Microsoft (or Apple or MPEG or Adobe or Netflix) fault it exists, it's the movie/show producers.
To make it "HTML5" somebody just needs to make a ABR client that will replace a browser's interpretation of the "video" or whatever tag Netflix uses on web pages. A set-top box doesn't need that, it can just connect over HTTP through a REST service to request the video manifest (the file that contains the URI of video fragments).