Sigma USA just issued a press release that their Nikon F-mount lenses has no issue with general operation when they are used on the Nikon Z7 and FTZ adapter. Sigma didn’t say anything whether they will release native Z-mount lenses in near future.
Here is another interview with Nikon executive for the Nikon Z6 & Z7 full frame mirrorless cameras. Nikon Z7 is now already shipping. According to the interview, Nikon is also working on low end models of Nikon Z series mirrorless cameras, may be APS-C(DX) size, below Nikon Z6.
According to latest rumors, Panasonic will soon announce two new full frame mirrorless cameras on September 25th. One is entry-level full frame mirrorless camera, the other is a high-end full frame mirrorless camera. Both has IBIS and 4K@60p. This means recently announced Nikon Z6 and Nikon Z7 will have serious competitors.