One can use the GH4 alone, even handheld - no cage, no accessories etc - and get decent 4K footage - to my eyes with less than 1kg, but it's not going to be a universal camera.
For documentary, if you have enough light it is probably sufficient. Use an external sound recorder for extra channels. Batteries last forever.
Here is my first ungraded tryout from when I bought the camera. The still/cover image shows the detail you get, the rest suffers from vimeo encoding. The 12-35 kit lens costs more than the body, and is worth the money.
GO TO VIMEO TO VIEW THIS, THE EMBEDDED VERSION IS HORRIBLE.
Here is another, this is with tungsten lights, handheld again ungraded
https://drive.google.com/file/d/0B1uQRKrjkUwdR096cjZHRXVIS1U/view?usp=sharingFrankly, if you want decent 4K with "still quality", the GH4 doesn't disappoint - the only issue I could find is that AF tracking is useless in video mode. As everyone here knows, I'm really random at shooting so if I get this quality of of this toy ...
Edmund