Anyway, by teamup, I pretty much mean Batmen United. I want to see Bats from Batman/Houdini: The Devil's Workshop team up with the JSA from JSA: Liberty Files. It would feature Nazi vampires, Italian werewolves and the first ever fight-before-team-up of two Batmen in trenchcoats. And Hourman has to fight off six werewolves before being saved by the JSA: LF version of Wildcat. Sweet.
Next, continuing the Batman/vampire theme I got running, I'd have the Dark Knight of the Round Table do battle against the Batman from Crimson Mist. It will be an epic struggle that will lead to the realization that the real villain is a rhymer from Hell, which would then guest star Etrigan while he was a servant of Merlin.
And it doesn't have to be just Batman meeting Batman, which would never get old, by the way. We could see the now infamous pirate Batman sailing the high seas with the also now infamous Captain Fear. Joo no joo wan eht. We could find out who's more badass; Batman: Year 100 or the Midnighter, which is really just Batman vs. Batman again, but we'll look past that. And how cool would it be to have In Darkest Knight Green Lantern (I have no picture. Let it go.) take on suddenly holier than thou Hal Jordan?
So bring on the multiverse. If only to increase Batman's lead in most comic appearances to date.