Looks like this will be announced next week. Rumored specs are basically a Z6 sensor inside a D750-like body, with improved FPS/buffer performance and Z6 like AF in video/live view. Same number of AF points as D750 when shooting OVF, and no connections for a functioning battery grip. Price about $2K.
A lot of people are upset about the lack of a grip option. Personally, I'm not sure how many folks actually use a grip on these cameras - I don't think it's all that many. But still this seems like a lot of $$ for what is really a fairly marginal upgrade, especially for stills shooters