Wait, wasn't Muppetfest a fan-run convention? Who are you going to petition?
And if you are serious, mailing a well-written letter to Disney people, times that by 1000 or however many people are interested, would be more effective than a petition in this case, as Disney probably has zero plans for a convention. Maybe trying to get details, and talking to them first, before writing a petition that comes out of nowhere, would probably work better.
I don't know how serious this thread is, but I thought I'd just say that.