To be more precise, Magit could easily display the output of difft, but Magit wants to be able to do more than that. You can navigate diffs by hunk and by file, you can collapse hunks and files, you can even select individual lines of the diff to stage or unstage them, apply or unapply them, etc. Strictly speaking that’s probably not impossible with difft, but because difft has the explicit goal of displaying diffs to humans rather than producing machine–parsable output, it won’t be easy. I still want it to happen though.