Although IntelliJ provides OpenAPI to add support for new languages, this is difficult to use. Netbeans started a new project called as Project Schliemann that makes adding new languages very easy. Also there is a 3rd party plugin in IntelliJ called as Simple Syntax that is easy to add primitive language support to IntelliJ. I think IntelliJ should also support Project Schliemann or it should bring its own generic framework for new languages. This will allow developers to use IntelliJ for any scripting/programming/formatting languages like LaTeX, AutoHotkey, Lisp and any other language else.
Link to Project Schliemann: http://languages.netbeans.org/