I think the feature mix of D7500 means two things. First, there will be a D500 successor. Second, there will not be a D5700 successor.
Back in the day the D70/D80/D90 did not have the AI-indexing tab. It was added to the D7000 when Nikon didn't think the D300 series would continue. So, at that time the D7000 was the top DX model. Now that The D500 is the top dog and has the AI-tab, they decided to remove it from the lower model again. This means that there will be another top DX in the future, D510 ?
Since the feature set of the D7500 is so close to the D5600, I think the 5000 series is dead. No grip, no AI-tab, no second card slot but tilt screen added. Sure, Nikon could name the next 3000-series camera D5700 but I doubt it.
So the Nikon camera lineup is now D5, D810, D750, D500, D7500 and D3400. Three FX and three DX. All the other models are discontinued, but unfortunately for Nikon, thousands upon thousands of them lie in warehouses unsold. I think the Df is also discontinued long ago.
Nikon manufactures cameras in batches and we can be assured they will not re-tool their assembly lines to make another run of D7100 or D7200 or D3200 despite those being still present in price lists. Nikon has way too many of those, no need to make a single one more. This can easily be evidenced by the current financial turmoil in Nikon.