Agreed. Cameras are so advanced these days that the manufacturers are struggling to top them. Will be years before I need to upgrade my D750 as it's just so good.
That is true. A lot is just down to physics. Sensors are already now so sensitive and have such low notice floors that within the shadows they are differentiating between a couple of photons. They are pretty much individual photon counters. Similarly with resolution, we can move to 54MP FF sensors but that is not that much better than 36MP and we already hit diffraction limits in scenarios where we might want to use higher resolution. E.f. you shoot at f/11 you wont really see a difference between 36MP and 54MP. If you shoot at f/1.4 you could, but then most of the photo is out of focus anyway. Metering already blows me away with how reliable it is, some improvements using more machine learning but ultimately when a camera makes a mistake its because it can't read your mind these days. AF could be improved but we start entering the physical limits of what a viable lens can shift focus at.
the real resolution is still a while away but it wont be hardware but software. Computation photography and computer vision, machine learning etc. will all produce the next steps. We are already seeing deep learning being used for intelligent noise removal or for up-scaling images. There will be things like combine multiple images in order to reduce noise floor or allow different Depths of focus and choosing focus points in post-processing. Photoshop's ability to make intelligent corrections will increase vastly in the coming years. Motion and camera blur will be able to be removed in lighroom automatically.
The face of photography will change because it will require even less sill to produce stunning results.