Update 9/4/2018: Kelvin has pointed out that there is evidence that the problem he points out below is actually a Sony ghosting problem with the A6000, A6300, A6500 and A7's. See this article for more details.
Kelvin from Bigsky Country sent me the example to the right and says:
In light of Nikon’s announcement last week, I'm wondering if I should buy another Sony A7R series camera, or wait for the new Nikon Z6/Z7 mirrorless. I did an actual lens test on an issue that’s been bugging me for a while. Certain combinations of lens/cameras I use render flare and light bloom in different ways, and some are just horrible in certain situations.
The rest of the image is just fine with any of these combos. This is a photo that compares the flare off of recessed pot lights in a typical home. I’d say the Nikon 14-24 f/2.8 smokes the rest of my ultra-wide lenses, making it worth my while to consider the new Nikon. I’d be interested to see somebody post a similar comparison with other commonly used RE lens/camera combos.
Your comparison test confirms my understanding that the Nikon 14-24mm f/2.8, for a very long time, has been the highest quality wide-angle lens on the planet. It is interesting that the Canon 17-40mm f/4 appears to be a close second. It is also interesting that DxOmark.com gives the Nikon 14-24mm a lower rating (31) than the Sony 16-35mm f/4 (33). So much for DxOmark ratings!
As for using the Nikon 14-24mm f/2.8 on the new Nikon mirrorless Z6 and Z7--you can get adapters for both Sony A7R series and Nikon Z mount to use it on either mirrorless body.
The bottom line is for those who have a Nikon 14-24mm f/2.8, you probably can't get a better wide-angle lens.