Sorry, I'm going:
I think you have hit the nail on the head with the corner sharpness of the 17-35mm. When discussing corner sharpness on land, the 14-24mm gives pretty sharp corners at f/2.8. Even the inexpensive 18-35 f/3.5-4.5 does pretty sharp corners at f/4.5! As do many other Nikon and Sigma primes. As you say, the 17-35mm does not, unless you close down the aperture to f/8-f/11.
The Sea & Sea correction lenses are a very interesting idea and something we haven't discussed here. I have found that they add around a stop to the 16-35mm, when used with a big dome. It will be interesting to find out whether the D850 will pick up the (deliberate) optical distortion caused by them. This definitely needs testing!
I tested the Nikon 20mm f/1.8 (http://wetpixel.com/...angle-lenses/P3) with the D800 and found it OK at f/11 or so. It was good for big animals in the blue, but I found the 16-35mm f/4 better. This is particularly true when the 16-35mm was used with the Sea &Sea correction lens.
The best performance that I have found is actually a legacy lens. The Tokina 17mm f/3.5 is, for some obtuse optical reason, a great performer. Here is an image taken with a 170mm dome at f/6.3:
(Nikon D800, Tokina 17mm f/3.5, Zen 170mm dome, two Seacam Seaflash 150 strobes. 1/200@f/6.3, ISO800)
Again, I have no idea how it will perform at 46MP. My gut instinct is that it will not be good as it is an old lens that simply was not designed to capture this level of detail.
Minimum focus distance is an interesting statistic. Remember that the lens needs to be able to focus on the virtual image created in front of the dome. The virtual image extends from just outside the dome itself (for very close objects), to 3.03 times the radius of the dome (for objects at infinity). So for a wide angle scene with the subject at infinity and a 230mm dome, the lens need to be able to focus 348.45mm (1) in front of the lens. Obviously, if an object is closer than this distance, the lens will need to be able to focus on it.
Apologies for going "off the reservation!"