The lowlight capabilities are really impressive.The Black Magic 5 inch HD monitor/recorder is pretty nice, we have one at work. Just make sure you pick a model of A7 that doesn't overheat and shut down.
You will need to use ND filters for some things with the A7S, but it will open up a lot of low light options.
I though the A7 had 14 bit depth but that is only for still photos. I guess its just regular 8 bit for video. The lowlight capabilities are still better then the GH4 and it has a full frame. That is going against the GH4's 4k resolution. Still undecided.
That recorder is nice though.