Rendering a movie is not suitable as a proof of work function. It's probably very difficult to design a mathematical framework to verify that you really rendered the movie and not just send garbage back in exchange for coins.
At the moment most Coins use either one or multiple hashing functions¹ or prime chains² as proof of work system³.
I think one of the harder problems would be verifying that the render results from a distributed system are correct, and then Pixar would be a centralized entity doling out coin for correct output. Unless there's some decentralized way I'm blissfully missing.
What if people started a Pixar road, where drugs and guns would be sold for Pixar coins? Pixar would have no control over that what so ever. I don't know about the technical part however, it could probably be possible.
What stops e.g. Pixar from opening up Pixarcoin where they let the community render their next movie? Am I missing something here?