Isn't there a KSP thread?
And yes, very difficult, given there's no framework for it to begin with. It's not as simple as adding in a model or coordinating two instances of the game to overlap...it's figuring out a plethora of behaviors to fit the game mechanics contingent on a variety of variables and conditions (when is send shuttle to mun?), then coding it in such a manner so as to be both streamlined and believable.