I think you could probably do this as long as the IDE understood an external project file format like maven — getting rid of IDE specific configuration files is a big win. Otherwise it is hard to know what the dependencies are in order to allow for intellisense and refactoring.

As soon as you do that though people will ask for plugins and then people will make plugins and then you'll be back where you started. IntelliJ isn't much more than a project file format, an editor and a plugin API.