I see a lot of posters saying 'yet' when referring to their favourite non-Apple video app notbeing ready for Airplay. Sadly, I'm reading on TUAW amongst other places that the documentation to add Airplay to 3rd Party apps does not exist. In plain English, Apple isn't letting developers add Airplay to their apps at all.
Yet.
But as the documentation isn't even there to get cracking on it in advance of Apple letting you do so officially, that suggests that Apple has no big plans to offer the functionality in the near future.