Yeah, Emacs may already be the Next Great Editor and not know it yet ;)
It needs to be more novice-friendly, having pre-CUA [1] shortcuts and terms ("windows" & "frames") is a trivial but powerful obstacle, I think. It needs to modernize its extension language: I still can't believe a 'then' clause needs a 'progn' if it's to contain multiple statements, but 'else' doesn't. I'm crossing my fingers for Guile, which, though still a niche language (Scheme), is at least more modern and standardized. I don't know how robust the interaction between the elisp (which is, like it or not, is here to stay) and Guile code is.
Emacs has a humongous codebase at over 2M lines of code [2] (of which, admittedly, 1.5M of that is elisp), with some deep black art as legacy from what it needed to run on when it started (thanks to ESR's work, the git history actually spans the entire 30 year history of the project! Here's the very first commit: [3] [Though admittedly because of RCS's per-file semantics, the early history is a bit weird).
But more importantly, it needs more mindshare. I'm hoping the git transition can help that.
[1] http://en.wikipedia.org/wiki/IBM_Common_User_Access
[2] https://www.openhub.net/p/emacs (slow server)
[3] http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=ce5584...