>>2685939From personal experience, there are a few reasons.
I really like the aesthetic of the sony A7 cameras videos. That, combed with the S-Log3 of the new MKII, along with the extreme low light performance of the A7S in general, just gives a stupid dynamic range, which is really going to be helpful. Plus, I can still use it for photos if need be, and ti gives me a chance to get my feet wet in the alpha series.
Plus, it's a full frame sensor, opposed to the M43 of the GH4, and I've never been a fan of the form factor of the BlackMagics.