The current AirVideo API are private and can’t be used by non Apple developers.
Jailbreaking developers have written a small hack that proves that AirPlay can technically stream third-party video to the AppleTV2. So do not despair to get AirVideo from your prefered application sometime next year without resorting to Jailbreak your iDevice.
I personally think that the new AirPlay for third-party application will be made available when the iPad2 launch in 2011. Maybe the iPad2 will have some exclusive game video to AppleTV integration? I speculate that such a feature might require a new processor that can handle encoding of output video on the fly for proper streaming to the AppleTV2… maybe through a multi-core CPU design with dedicated screen output to mp4 transcoding?