Thanks for the answer!
I wish there existed longer telephoto lenses for MFT though. I know they're not needed for most common filmaking situations, but for wildlife documentaries...
That being said, a crop mode in the GH4 could do the trick. Or cropping 4k footage in post.
Speaking of DSLR vs mirrorless, I'd love to say goodbye to the monstruous Z-finders and use a proper electronic viewfinder (or articulated screen)!
Remember, we are still in the days when Vimeo recommends you downscaling your uploads to 720p for better playback performance. There's nothing worse than a stuttering video or one that stops in the middle of the action.
The future of video might be 4k, but it will also be streaming. And speed connections, generally speaking, still need to improve.