Emacs seems to be a local maximum that is difficult to overcome. An entire Lisp Machine environment would be better, but it would be a tremendous undertaking and the specialists, i.e. emacs devs, don't seem to be interested in such a thing.

A multithreaded version of emacs would also be an interesting addition; I read some arguments against moving emacs to a multithreaded model, but I don't really remember them.