From an interoperability perspective, even if WebRTC & CU-RTC-Web end up competing there will be JS libraries out there that will support both. So it seems SDP is not the big issue here, but there is an elephant in the room, the media stack
Differing media stacks (specifically codecs) could cause big problems. As an example; IE & MS endpoints may support various Microsoft codecs versus WebRTC compliant endpoints (Chrome, FireFox, Opera, Mobile Apps etc.) which would presumably support the RTCWEB MTI (mandatory to implement) Video and Audio codecs.
That is if WebRTC has such codecs. We still don’t have a MTI Video codec yet! <- This has been one the most contentious issues in the IETF RTCWEB working group to date.
If we fail to deliver a MTI video codec in WebRTC what’s the likelihood of opposing browser vendors (implementing opposing standards) supporting the same codecs? Not very good odds I would expect. In which case cross-browser communication (media: audio, video) would fail.
Although, we might get lucky and have all the browser vendors select at least 1 like audio and video codec on their own accord. Ya, right.
If you don’t want to leave it entirely up to chance, get involved! Joining the IETF is free and open standards need your support if they are to succeed. The next IETF meeting could be be very telling wrt a MTI video codec: http://www.ietf.org/meeting/86/index.html