While I think always-on connectivity where image transfer is automatically taking place in the background (instead of wifi where the connection has to be re-etablished after the camera has been off with iOS devices) is important, from what I've read it doesn't work as well as expected in the Snapbridge enabled cameras that are out so far. Rather than introduce more cameras that support this technology, Nikon should improve it to the point where it works for 90% of the users and smartphones on the market, or revert back to a different technology which works better, and only when the technology has been implemented in a near-universally approved and acclaimed manner, then spread it to other cameras in the lineup. I fear that Nikon risks ruining its reputation by bringing out this technology in more cameras before it is mature, fully functional and reliable.
The touch screen in the D5 works ok for reviewing images, scrolling and zooming. I use this at times. Implementation of the scroll bar functionality in the D5600 seems sensible.
Another feature which should be implemented in the D5x00 series particularly is better live view AF. I see people using this series of cameras often out there, relying entirely on the LCD for composing and timing their images, and I think many must be frustrated at Nikon's LV AF performance. Canon has made great progress in this area with their latest dual pixel AF system and I think it's vital that Nikon show that they can do something similar as well, so that the use of the camera for either photography or video, when taking advantage of the flexible LCD screen, becomes more fluid.