The picamera library permits unencoded video recording and image capture by specifying a format like
rgb. See the start_recording method for details.
That said, I'd be very surprised if you could record such a stream at 1080p to the SD card. For example, let's assume you've got a class 10 card (i.e. one capable of writing 10MB/s). At 1080p (1920x1080 at 30fps) with RGB (3 bytes per pixel) format you'll need to transfer:
1920 * 1080 * 3Bpp * 30fps = 177MB/s
Even if you go with YUV which cuts pixel size down to 1.5 bytes per pixel you'll still need 89MB/s. Given those numbers it's unlikely you'd even be able to pipe frames over the LAN. The only way to get it close to 10MB/s is to cut down the resolution or reduce the framerate.
In other words, you'd be much better off experimenting with an H.264 stream first to see if it's good enough (I'm always wary of claims that things won't be good enough without actual experience to back them up). Switching from an H.264 stream to an unencoded stream is trivial (at least on the picamera side), although you'd then need to tackle the question of bandwidth...