This is coming from somebody close to Nikon development (new, anonymous and unconfirmed source):
"He/she told me that he/she has been working on firmware that only supports video. Namely, his/her area is autofocus through the sensor. He/she told me to think of it as tripod mode in Live View but that it was much more complicated. Apparently speed is important and an area that is out of focus can be selected and the lens be made to jump to focus in that point in one move without hunting.
He/She told me that this required distance data and AFS from the lens. As far as I know, all AFS lenses support distance data but I'm not sure.
At any rate he/she says there's hardware support for h.264 encoding. He/she also said that there is support from increments of 24 fps and 30 fps (so 24, 48, 72, 96 etc. and 30, 60, 90, etc) but I didn't ask how high.
He/she said there would be no support for still image captures though it's all progressive video which lends itself (a bit) to having still images pulled from video.
He/she said 1080p, 720p, 480p, and 320p (?) are supported.
I was discussing trading up from my D300 to a D300s just for the video support and he/she told me to wait. He/she said that there wouldn't be anything soon but it would be in the lifespan of a D300s.
I asked him/her if it was a video only f-mount body. He/she told me he/she had very little knowledge of the hardware.
He/she did mention working with a team that is developing a NEF equivalent for video. Which was very high in bitrate necessitating high end media. He/she didn't know if it was CF or SD."