As a Z6 user, this is definitely a camera that I have on my radar. The Zf didn't interest me much : it was too big for what it was set out to do and the situation I'd use a Zf in, I would rather use my X-Pro2 or Oly E-M5 mark II.
However the Z5II is basically if they put a Zf in a Z6III body. Same sensor as my current Z6, but flip out screen, 10bit video and modern autofocus.
Only gripe so far, is that if I bought a Z5II to make my Z6 step down towards the "backup camera" role, it would still be the camera I reach for for some occasions : funny enough, those where I need a long buffer.
The CFXB card slot of the Z6 means that the buffer issue is basically written off : a full buffer is written on the cars in like 1-2 seconds, I don't have to wait before shooting again, which makes it really nice for sports shooting. The Z5II still has dual "regular" SDs, which will take much longer to write down the same kind of buffer.
I guess if I was a Z5 user without any CFXB cards to care about, I wouldn't be in such a pickle.
If only the Z6II had an Expeed 7 processor !