I have - but it's not pretty, because remappers have images of the mapping displayed on the screen, e.g
Jump - [A] (as an image, rather than Output 13 or whatever)
In order to do this, I need the mappings!
In addition, there are a lot of fun little games out there, and it should be as easy as humanly possible for players to just pick up and play - few games force the player to involuntarily remap (edit: map inputs to outputs) immediately, as this is hassle.
So I disagree.