in video mode the frame will be 16:9 so the biggest they'll get is 53mm x 30mm vs Full Frame which is 36mmx20mm in 16:9.  It's a significant increase in sensor area, however I bet they window in.  - the 11,000 pixels of sensor width skipped down to 3800 will not be nice!.  Assuming they do use the full sensor width the horizontal crop factor is 0.68x.  When the lens speed tops out at f2.8 on Hassy's boring lens line up a 5dmk3 in raw and some otus's are likely a better bet for achieving the look