I watched one useless and incomprehensible YouTube video that screamed about the stupidity of the Z50 release, but within the same video he lamented all DX crop shooters who use FX glass because "you're wasting light" - his exact words, not mine. But outside of the who's saying there's no market?
Will we see another pro level DX? Probably not. But when you have 50-60MP mirrorless cameras cameras that can deliver 20MP's in cropped mode with the EVF cropping as well, you probably won't see another one. But a "market" is defined by what's available at what price point. I think Nikon would be utterly foolish to drop another 3xxx or 5xxx series camera, and I vaguely remember there being a rumor that this wouldn't happen. If they do another 7xxx camera it will probably parallel the D780 in that it'll be a D7500 with a Z50 sensor and mirrorless functions available in Live View - effectively a mirrorless for someone slow on the uptick or otherwise unwilling to make the change.
I saw a review of CES that spoke of the Canon 1Dx Mk iii as probably being the last major DSLR release you'll see by Canon and I believe it. Mirrorless tech is finally such that you don't need the optical viewfinder any more, and you are getting functionality you could never implement on a DSLR. Add to it that smartphone cameras are growing in leaps and bounds the market is going to squeeze into mirrorless-only over time when it comes to anything that you don't text your friends with.