I think a live action Calvin & Hobbes movie would be awesome. Cast a blonde haired little boy to play Calvin, and constantly CGI his daydreams and imaginary adventures with Hobbes.
I remember, years and years ago, there was a movie starring the late Gary Coleman (back when he was a big star on Dif'rent Strokes) as a kid who was constantly daydreaming. It was actually an espionage action/comedy, kinda like the movie Cloak & Dagger, where he has an important piece of stolen government property but he doesn't even realize it. Then these KGB agents keep trying to take it from him, but he keeps using his daydreams to come up with ways of escaping. For the life of me I can't remember the name of the movie, but a Calvin & Hobbes movie done in a similar vein would be a lot of fun.