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.
> I read some arguments against moving emacs to a multithreaded model, but I don't really remember them.
Everyone including the maintainers would like this to happen. The arguments against it are technical hurdles. Emacs is a large ball of global state and the lisp evaluator hooks into everything, including the display engine, so it's not clear to anyone how to disentangle things to the point where the interpreter lock can be released.
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.