I'm waiting to hear the reviews from you early adopters. I'm torn between the GH4 and the Black Magic. GH4 is more afordable but I'm still unclear as to what color space it records 4K in. I think its only 4.2.0 which makes the video harder to use for greenscreen stuff. I would like to have at least 4.2.2.
You can get 4:2:2, apparently, but only with an external recorder (like the Atomos Ninja Blade). Internally, it's 4:2:0. Some note that 4K of 4:2:0 can be downsampled to 4:4:4 1080p in post, but there may be compression issues. The GH4 records 4K at 100Mbit/sec and 1080p at 200Mbit. Both are excellent data rates in general, but still less than the Blackmagic Pocket uses (220Mbit for 1080p). Encoding matters, but less data ultimately has to cost something.
Having said all of that, I think these are two very nice 1080p options, but with vastly different operating experience. The GH4 will be (don't have one yet) a pretty user friendly setup and I expect the 1080p out of it will be terrific and significantly better than that from the GH3 (4K doesn't really interest me at this point). The BMPCC produces some really wonderful video, but lacks a lot. ISO is limited (the BMPCC is not a low-light or even dim light solution), focus and exposure setting are just rudimentary, you can't format a card in the camera or see how much space is remaining, battery life is terrible, etc. But having said that, I think for flying the BMPCC is very very nice. And if DJI would get their BMPCC zenmuse out the door I could say for certain if that's true. It's pretty much a given to fly in manual exposure mode, in good light, with fixed focus, etc. So for this purpose, the BMPCC's limitations are not really a problem. For on-the-ground use the GH4 might be the winner -- not because I expect the video will be any better, but just because the handling and UI will be so much more developed. Plus, on the ground it will be easy to use a secondary recorder like the Ninja Blade to get the full quality that the GH4 is capable of capturing.