I guess I should really participate in emacs-devel a bit more, but I've always been in favor of allowing Emacs to support multiple languages with a common runtime. Emacs Lisp is slow, that's true, but there's no problem intrinsic to its syntax that makes it slow. Similarly, there's nothing intrinsically slow about the runtime that Emacs provides; it's a bog standard dynamically-typed language with the slow stuff impl…
I think one of the strength of Emacs, that has allowed it to grow that much compared to Vim, is that it has always had one official extension language. It doesn't have any external dependencies. If Emacs developers endorsed extending Emacs with other languages, users would have started using other languages libraries, which could have caused issues in portability and set up.