Admittedly, many of the D500's strengths are a greater advantage above the water. One feature that is fantastic wet and dry, though, is the autofocus. Not only is it superbly fast and accurate, you can select your focus point over basically the entire frame. The wide field of focus is something that was previously only available on mirrorless cameras.
Regarding wide angle, I don't think DX is a negative at all! The reason? Tokina's fisheye! Put the 10-17mm behind a mini-dome and you get a fantastically versatile (and small!) wide angle rig.
You can see the entire album shot with a D500 here: https://flic.kr/s/aHskUBxNdh
I really enjoy mine, and don't regret housing it.