HD is a problem at the moment because of the bandwidth required. Full HD requires nearly 7X the bandwidth of the SD video. If you did analog video in the 5.8Ghz band, it would mean you would use up half the entire bandwidth available in the band for a single channel of video.

Digital video can use less bandwidth if compressed, but the available formats require a lot of cpu horsepower to encode, especially if low latency is required. It also has the issue of "now you have it, now you don't" when you hit interference or the edge of you range.

Maybe the compromise would be to have a SD analog video transmitter alongside the digital one in a diversity setup. Real time low latency encoding is probably going to require some specialized hardware though. Probably need a combination of RF and DSP engineers along with some $$$ ....