How do you keep an idea alive?

Been working on my next story, but it's been difficult. First just getting started has proven to be a challenge, as I'm not sure how to fit it into the template that is MLP:TM. I've always felt that the movie was full up to it's eyeballs in plot holes, but just how does one fill them in a way that makes sense? In trying to do so, I've run into another problem, namely that it requires so much backstory that it adds an awful lot to my workload, and that takes a toll on my enthusiasm. Well, maybe the key here is to wait till after Christmas at least, and see if that helps. I've got a couple good new characters here that I'd hate like hell to not use.