Problem is you couldn't run it in the AoK playback system.
It would have to be a super-long movie. Now, personally I wouldn't mind. I have a good ethernet connection and would just let it run all night. But to other this would be ridiculously big.
Add to that the fact of ES doesn't want us to know very much yet. They are realising details just a little bit at a time. I doubt they would release an entire game's worth of video. (Although I would welcome it if they did. )
"It may come as a shock to you . . . You can have fun and be serious all at the same time."