I just bought a new Nauticam housing to fit my 1-year-old D850. This is an upgrade from my Nauticam D810 rig I'd been using for the past 3 years. I also replaced my V24 Fishlite focus light with a Kraken 3500. Nice light with amazing battery life. Kept the YS-D1 strobes and arms.
Why? Because at 65 I may not be able to soon, and I wanted my best underwater. The D850 specifically gives me better autofocus and a few more pixels to crop with. I shoot it with the same two lenses I've been using the last 3 years, a 105vr for macro and a 16-35vr behind a 230mm dome port for wide angle.
I've tried a few things that didn't work for me. 60mm macro and matching port. Used one dive, working distance too short. 1.4 teleconverter and 30mm extension ring. Used two dives, not sharp enough. +2 diopter for the 16-35vr. Used half the time, never saw a difference. Edges and corners terrible.
I also just added a Sea and Sea 77mm Internal Correction Lens to my 16-35, and it has transformed it! This is a winner, big time. I'll never shoot the 16-35 underwater without it again. I can get away with shooting wide open at F4 now and not even have to crop the corners. Worth every penny.