I don't think you can really even compare the situations of Harry Potter and Avatar. I see this being more about the theme and story plots from the Avatar Universe instead of bringing any characters from the movies into the land like WWOHP that is based on a character heavy movie/book series. The characters don't mean as much in a movie like Avatar as they do in Harry Potter, so it'll be all about how WDI can nail the theming and story. If they can do that, they are already in a pretty good spot...