my panasonic gh4 doesnt have this problem - of course its a dslr-style mirrorless camera. i can shoot as long as my battery lasts and have never had any overheating. this is likely due to its smaller micro 4/3 sensor size
looks like an awesome camera. canon has covered most of the bases - just wait till the price comes down. its already 12k on b&h. the blackmagic has similar specs but there are serious reliability problems with their camera (while we know the canon will be a tank) and after shelling out for the blackmagic viewfinder, battery, battery mount, shoulder kit, etc, you're spending close to the same anyway. you wont have the codec problems of the sony fs5, the overheating and battery problems of the a7s/a7r series. im still sticking to my gh4 and soon gh5 as im invested in the lenses and accessories (internal 422 10-bit will be plenty!!) but maybe down the road when i'm making more money.
guys, ive been shooting paid gigs with my gh4 for over a year now and i can say unequivocally, the image quality is definitely NOT crap. just look on youtube or vimeo at examples. in fact with the right settings, it offers stunningly good results. the 1080 internally processed slowmo and timelapse are awesome. no its not great at low light, but with a speedbooster and a fast lens its perfectly fine. the gh5 will offer 422 10-bit internally, 5axis sensor stabilization, better autofocus in video mode (very anxious to see how good this will be mainly for gimbal work), 180fps 1080 slowmo, much better low light performans and dynamic range and much more. battery life is much better and sensor doesnt overheat like the sonys. the only reasons i see now to go with sony are the extreme low light performance and the greater depth of field - the full frame look is still great, although u can get a nice super-35 look with the gh4/5 and speedbooster.
the codec stuff is great, but the gh4's biggest weakness is noisy low-light performance. come on panasonic! you can do it! you have to compete with low light monsters like the a7sii. good facial tracking auto-focus in video mode would be awesome, and push up those frame rates! and how about an xlr input while youre at it?