"Right now WebM is not comparable to H.264 except the baseline codec."
It's comparable in the sense that AAC and MP3 are comparable. VP8 can look excellent, it's just that high profile h264 can look better at the same bitrate.
It's also extremely likely that youtube uses h264 baseline profile anyway, since they serve to mobile devices (unless they secretly transcode and store multiple h264 versions for every video).
Pretty much every video content provider I know does this. I work primarily on OTT Boxes (Roku, Boxee) and Connected TVs and all of those platforms support bitrate selection of video assets based on a speed tests. I'd assume most platforms doing progressive download of video over HTTP does the same.
It's comparable in the sense that AAC and MP3 are comparable. VP8 can look excellent, it's just that high profile h264 can look better at the same bitrate.
It's also extremely likely that youtube uses h264 baseline profile anyway, since they serve to mobile devices (unless they secretly transcode and store multiple h264 versions for every video).