The only thing that could achieve such a thing would be a device with iOS levels of popularity that a) doesn't support h.264 b) doesn't support Flash. Who is going to make such a device? A: Nobody, because it won't support any web video at all apart from maybe YouTube.
You can grouse about open principles all you want, but the big video producers don't care; they will not be a factor. Audience demand is the only thing that matters, and they won't demand WebM when h.264 is already working "fine".