This will fall to the curse of most people answering didn't write emacs. That is, rewrites can work sometimes. You typically need someone who was involved in

This will fall to the curse of most people answering didn't write emacs. That is, rewrites can work sometimes. You typically need someone who was involved in the last two for it to work, though. If you haven't written it once, you have no real idea on any compromises that were made. If you haven't tried to do it without a compromise, you don't know which compromises were unexpectedly vital.