It would require further compiling an X server or Wayland, the Lucid GUI toolkit, freetype and fontconfig, a bunch of image libraries and maybe more stuff I don’t know about, plus of course all their dependencies.
It would likely take some effort to get X or Wayland to refresh the screen responsively, possibly using xdamage or Wayland protocol stuff to intelligently ask fbink to do limited refreshes.
The keyboard and touchscreen might be configurable but I haven’t done it. If it turns out to not work out of the box another option besides fighting drivers would be to be translate the event devices in /dev/input into virtual devices like efbpad kbreader does.
GUI emacs seems doable and requires, in my estimation, about “this project” again more work. The issues with the terminal version should probably be resolved before continuing. I’m unsure how much less responsive it will be than the terminal one.