From the info out to date:
No AI indexing
No back focus button
Only one SD card slot
Will it be capable camera, I don't no reason to doubt it will be.
Owning some AI lenses, its important for me to have that functionality.
Using back button focusing all the time, its a feature I consider mandatory.
With the video capabilities, it sure would have been nice to save photos to one card and video to another.
Circular viewfinders simply makes a great deal more sense.
My points are not specifically related to the underwater photographer, but photographer in general.
The bottom line from my original post is, price wise and stable wise I think Nikon missed the boat.
You say the D7500 has no back focus button, but it appears to have the same AE-L/AF-L button as the D7200 which can be programmed for back button focusing as explained here. Am I missing something?