I say that instead of putting the ports on the back they should be moved at the front. If they want it to look pretty rhey could just cover it with something when the ports are not in use. Or at least add some important ports at the front and the rest behind. It would also be nice to make screen tilt to the other side. This would be useful when you have clients and want to show them something, you could just move it over 180 degrees so the other person can see it. Finally, USB C.
Not too much. New kaby lake CPU, new nvidia graphics card, full ssd, usb C options. A video input, so you can use the screen for another PC. I like mine very much, and won't likely upgrade to a new one unless it is a huge boost in performance.
USB-C with Thunderbolt 3. Input so it can be used as a dummy monitor. 10XX series of Nvidia GPUs, maybe a Intel Xeon CPU to compete with the upcoming iMac. Update the Pen to the new specs and full SSD and Microsoft will have a very powerful and beautiful new Studio. Keep the same form factor and screen.
If the Surface Studio had a truly matte display, it would be hard to resist. Its current, highly reflective screen is difficult to work with in many, if not most, environments.