Emacs mode already? They're doin it right. :)
I was not aware RStudio was web-based. News to me...
Yep, RStudio is GWT driven (https://developers.google.com/web-toolkit/) and uses some very particular configuration tricks to keep you from accessing it with a browser in local mode.
There is already an emacs mode for Julia: https://github.com/JuliaLang/julia/blob/master/contrib/julia...