Another thing to consider was that human!Princess Celestia is in Samurai Jack, too. Man, Faust and McCracken created their own little universe, didn't they?

Now, we all know Samurai Jack ended without a proper Final Showdown with Aku. What if we DID have that showdown, with Jack leading an army of Heroes recruited from across time and space? We could have the Powerpuffs, the Quest family, Dexter, the Kids Next Door, Team Venture, the Flinstones, the Jetsons, Yogi's Ark, Billy and Mandy, Secret Squirrel, the Foster's Friends, the Scooby Gang, the Eds, etc. etc. etc…