Something that I'd like to see that I don't think would be too hard to implement (course that may not be true) is that while the key assignment dialog is fairly complete, it's missing the arrow keys. I use a mouse that has the right and left buttons mapped to it off to the side, and I thought it night be neat to control the undo/redo features with it.
You could also add in special characters such as those located on numpads.