The main advantages Nikon will have over Sony are the 60mm flange mount that really sets it apart from the competition. Sony can't have very fast, low distortion low T-stop lenses with the small E mount, unless they abandon their userbase and change.
An MF style lens is simpler, fewer elements for fast and low distortion. Having a large mount means Nikon can have a fast action camera, studio high res MF body, a general purpose low light camera all sharing the same lenses.
The reported 5-6 axis in body image stabilization further lowers the complexity of lenses which help keep weight and cost down. The 58 f/0.95 will be enough to cause a lot of people to move to Nikon. I will hold out hope for an 85 or 100-135 range prime f/1.2. I would not be so concerned about adaptors, my D800 is not going away.
Another advantage is at the wide end, a large flange is a big help there so landscape and architecture shooters will move from Sony which will always be weak on the wide end.
Other pluses will be ergonomics will be FAR superior over the too small, too imbalanced and too uncomfortable a7r3.
Without much doubt, a Nikon will be built better than an a7 series, which really is cheap in construction, flimsy in fact with tiny plastic connectors, doors and no weather sealing at all. If it did not have all the features gadget lovers crave, but never use, at $2000 for such construction and discomfort would be a joke.
A lot of features of the a7 could be left off and no one but amateurs would mind. Eye tracking or focus peaking are two that are useless as implemented. Peaking is way too broad and ineffective on any aperture wider than f/2.8 and eye tracking assumes every shot is a conventional portrait when it gets it close. Getting the appropriate focal plane is better left to the photographer who has the advantages of knowing what his intended composition is or needs.
Rumors suggest just under 500 focus points. Again, I don't care much as long as it is over a wider area of the VF than current Nikon FF cameras. The D500 has a really good coverage.
Speed of the 24mpx Z6 is rumored to 20fps, and 10 for the Z7 46mpx. We will see in a few days. I never cared much for high frame rates, a lot of frames to examine with hi pixel count cameras.
Is it a Sony fab sensor or TowerJazz? Combining the very efficient backside illuminated tech with FAST lenses and Nikon superior noise and DR track record, these will be the low light kings.
Personally, I think the low light demand has gotten ridiculous....low light IS noisy and has little color information by the nature of light, regardless whether a camera is involved. There is less detail and edge acuity in low light, The colors and contrast is synthesized and not realistic when people try to use the low noise cameras as nightscopes.
In summary, the cameras will be a success if they have only a few things nailed:
FAST lenses
Great ergonomics
Rugged
great IQ
Weather tolerant
Decent battery life
Useful Video
Less than 2500 for the Z6 and less than $3500 for the Z7
Lenses and grip available at release
These items would blow Sony out of the competition.