If Apple isn't going to support it for iPhone and iPad, and you seek a common video encoding, you might as well say straight out that it isn't viable.
The cover-all solution for video is exactly what YouTube uses right now - Flash and H.264. There is absolutely no chance in the foreseeable future of eliminating the H.264 piece, because of Apple. There is some chance of eliminating the Flash piece, depending on IE9 becoming widespread and Firefox either relaxing their stance on H.264 or becoming irrelevant some day.
These facts make people upset, but they are facts.