1) A small roller ball on the right side center (the same kind that you see on the mac mouse or Black berry phones). Right now the only way to scroll around the pages is by using the finger. Which has two BIG drawbacks. One it makes ugly greasy marks on the surface and second: very difficult to navigate without two hands.
2) position of the plugs for charging, headphones are totally wrong.
3) additional 2mm charging plug right on the device so you can use most of the old Nokia chargers instead of this funny adapter. Most of the micro usb chargers for other devices don't work very well with the charging of this device.
4) IR port on the side so that usage as a remote is more intuitive (provided that the portrait mode is fully supported by the new devices right out of box)
5) DON'T ever make this stupid mistake of (mis)using the arrow keys for other characters like in Scandinavian keyboard layout for the HW keyboard. And to complete the whole blunder, put the alternatives for the up/down on the same keys as the left/right! If you want to save some space on the HW keyboard, refer to the point number 1 on my list.
6) Don't use the shining chrome bezel for the camera frame. The light reflects from it making the pictures hazy!
7) Remove the camera shutter button and use the scroll ball instead to take the pictures or make an on-screen button to take the picture.
8) Bring back the N810 style of kickstand with multiple positions and good sturdy hold on the table instead of current miserable small hook on the camera bezel.
9) Allow activation of the on-screen cursor using some other methods instead of this “hit and miss - drag the finger from left” implementation. From that point onwards, you should be able to control your mouse pointer using either your finger or the scroll ball.
10) Wouldn’t mind at all if the speakers were brought back to the front as in N800. Although the looks are not very pretty, the sound quality feels much better since they are pointing at you instead of sides (in most of the cases towards your palms).
Perhaps I won’t go into the most obvious improvements like capacitive screen or multi-touch capabilities etc.