I’ve also thought that the “numpad”-sized module would be great for a touchpad, and @Hugues_L is on roughly the same page as well.
There’s also a bit of work on a numpad-sized display module, and I thought that combining the two might be interesting – basically a touchscreen that you could use as a touchpad, but which could also provide some visual feedback – so you could use it as a small digitizer tablet for drawing as well.