For documentary work in the field, I think it might be best to think of this camera in terms of getting b-roll.
I've used a first-batch BMPCC as a b-camera for narrative work (and next week I'm sending it in for calibration to eliminate the white orb issue), and if I were to use it as a run and gun documentary camera, I'd certainly want a few extra SD cards - I'm getting about 40min per 64GB card, and probably a few more batteries. I currently have 9 and feel like that's sufficient for 6 or so hours of shooting. Audio isn't great, so rigging an external recorder and mic would be necessary. It would be a little cumbersome, but could work.
In this price range, though, you might be better off getting a GH3 or G6 for running and gunning documentary work - better battery life, fewer storage needs, better in-camera audio. Or, for a few grand more, jump to a C100.