Is it possible to have VP8 as a mandatory baseline on platforms that support it, so at least all desktop users could rely on having VP8 support in WebRTC, even if Firefox still has to support H.264 for WebRTC calls to/from mobile devices?
Yes, that is possible (technically), but again, in the view of people on the scene whom I trust, VP8 was never -- meaning extremely unlokely -- going to win MTI. Likely outcomes: no MTI or H.264 MTI.
No MTI would let peers negotiate, and VP8 does win against baseline h.264 on quality. Then the question becomes: will all the bigs support it? We do, and will.
