The only USP for a Nikon mirrorless camera at that size, would be a larger sensor. If the rumors are correct and the bayonet is 65mm, it's possible.
Fuji film GFX bayonet diameter is 65mm (internet spec) and the Hasselblad X1D diameter is 61mm.
Medium format (or close to) would make the Nikon interesting, otherwise, it's just another mirrorless camera, 5 years too late.
Does a larger sensor mandate correspondingly more heroic lenses or can adapters such as Metabones allow wider options?