A user on the forums, xracer, was doing some work on getting some HD xcom going. Watching him work on his mod, it seemed like you would have to write some code on every single display to get it to show up at the right spot. Otherwise everything is cramped in a corner.
The bulk of the work is definitely source code changes to the engine. A working HD engine will lure artists more than HD art will lure programmers ;p
The devs are also very helpful, and if you do undertake this task they will help you where they can.