Im afraid Nikon will be too conservative with their FF mirrorless system. It needs to include every available technology. This was not the case with the new D850 - no IBIS nor high resolution mode - the half-priced Pentax has them, why not Nikon? The Sony mirrorless products have IBIS, so why didn't the D850? The Nikon 1 system was fantastic technologically, but wasn't a professional/advanced amateur system in that there was no weather sealing and some models shipped in multiple colors - indicative of toys and not something a pro will necessarily want to carry, nor be associated with.
What I'm looking for in a Nikon mirrorless system:
Outstanding weather resistance on the bodies, lenses, and accessories (no exceptions);
IBIS;
High resolution mode (sensor shift);
built in wifi, bluetooth, GPS, and compass;
(oh, and since it has GPS, the user should at least be able to do simple navigation from the display with a global map);
gyros/levels in every axis, so I know level and can easily use it as a copy camera or pointed parallel to a ceiling;
smart lenses (like micro-4/3) where lens corrections are effectively built in, with the best manual focus feel, and smart focus stacking;
a mark on every lens that indicates the approximate nodal point;
a collection of small (Otus quality) prime lenses that are weather sealed for travel/expedition; and,
As well as many other out of the box things, how about a dedicated monochrome camera!!!!