We've just had a major codec battle about 2 years ago for HTML5 video, and I believe it still wasn't decided. Why would we go through that again? Especially when they want to add a proprietary codec to it.
Other CU-RTC-WEB aspects like the ones which focus on providing more customization as to how the network transport is handled could be integrated with WebRTC, this would allow more control over how the media is handled in transport, CU-RTC-WEB doesn't specify which codec to use so the final standard might as well just choose webM and opus.
