Where the Ninja 2 crushes the Video Assist is the fact it records to HDD/SSD. For fixed cameras recording a long event, those big fast SDXC cards get expensive.
The A7S II Sensor will come in a DSLR sized body. Sony, Panasonic, Samsung have already shown you don't need a big camera to handle the 4K video encode.
And those people going the Ursa/Ursa Mini route will quickly find they need to budget at least $4K for the CFast cards. Two being ingested and two in the camera. And of course you need lenses. And a boat load more computer storage and backup. Is it still a compelling choice? For many it will not be.
I'm more likely to see if I can 'scrape by' with an Atomos Shogun instead.
Unless I've missed something, to record internally the camera must be in 8-bit mode, not 10-bit. So if you attach the YAGH interface in part so you can record 10 bit externally, you can't record internally at the same time. On the other hand, if you stay within the confines of an 8-bit codec, your golden recording internally & externally.
Of course Panasonic may have changed things in the Version 2.0 firmware which I haven't tried yet.