I was about to upgrade to the Nikon D500 (from D7000), but Nikon announcing the D7500 has made me pause for thought...
It looks quite promising...
D7500 has inherited a few things from the D500, including the same 20.9 MP sensor and faster processor (burst speed, buffer depth, ISO sensitivity, video) but same 51-point AF system taken from the D7200. 4K video, with the same 1.5 crop as the D500.
Has a pop-up flash, but that's not really an issue with most housings having flash triggers etc. The recycle time of the pop-up flash will still probably be the slowest part in the equation, meaning that a flash trigger will still be a quicker (and more costly) option.
Will be interesting to see the upgrade price (camera + housing) for the two cameras.
http://wetpixel.com/articles/nikon-announces-the-d7500
https://www.dpreview.com/news/2885741290/nikon-d7500-what-you-need-to-know
Good to get thoughts from D500 and D7200 shooters...