[@Mr Allen J]

On a serious note, if you're worried about how some shows might now fit into a shared universe (e.g. Steven Universe is an AU Earth, Camp Lazlo/Gumball/Regular Show features talking animals, Samurai Jack is another AU Earth...), there is a Cartoon Network original that could be used as a MacGuffin to make it all work.

[b]Uncle Grandpa[/b].

He's intentionally universe breaking, and the writer's have used that to bridge their shows into a sense of shared multiverse in the past. For example, when Uncle Grandpa appeared in Steven Universe, he had a checklist that referenced everything from Clarence to Adventure Time. 

So, the concept of a Cartoon Network multiverse is already out there. Which makes it an easy set-up for what you are proposing. In that sense, it could almost be like Kingdom Hearts (taking place in original places and in worlds based around a series/franchise).

Just my 2 cents.