They've never put out criteria for what is and isn't considered, but while Star Wars and Marvel are theoretically possible, I don't think they're probable. They tend to stay away from live action characters. Besides Muppets, there has only been a handful of PTDs from non-fully-animated movies - Giselle, Narissa, Edward, and two Pips from Enchanted, and a penguin waiter from Mary Poppins. There has yet to be a PTD from a fully live-action human character. I think if they do do Marvel and Star Wars, they will probably stick with animated/comic book versions of the Marvel characters, and the muppet/droid characters from Star Wars.