I would say expect 16mp, a deeper buffer, maybe a FPS speed bump that will be more academic than mind-blowing, perhaps new processing engine (like they did with the D2hs) and a host of other internal electronic tweeks that don’t involve the photographer.
Look at the D70/D70s, D300/D300s, D2h/D2hs, D2x/D2xs and D3/D3s comparisons and you’ll get an idea what to expect unless Nikon goes “off the reservation” and surprises everyone… ((chuckle))… don’t hold your breath on that note.
I think usually the “s” models are cameras that benefit new buyers buying into that particular model number for the first time, the most.
One thing for sure, just seeing a new pro body from either of the big two will be something neat/interesting to peek and poke over and read all about…. Someone go wake Canon up, the more products/lenses to read about the better 😉
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.