According to Andrew Reid the 4K mode has a FF crop factor of 2.7x which translates to a FF zoom lens equivalent of 37-592mm, so not very wide at all. I am hoping this means that the 4K image will be very clean with very little aliasing and no moire. ( I suspect the extra crop comes from the FZ1000's 20 Mpx sensor vs the GH4 16 Mpx sensor )
Andrew has this slightly annoying habit of not clarifying things at times. I'm not sure if he's held the camera in hand to test. I'm going to wait till he answers the question another user asked about it, since I haven't seen Panasonic saying it's a direct crop without downscaling.