I really like the idea of having something common like that across servers. It would make the separate server seem more like they were in the same world (just different cities.)
That's actually the part I like about the idea, it's a very small movement towards relating the servers to each other. Once you think about them being in the same world, you might be able to expand the idea to some type of cross-server communication between the cities, which I'm sure would make the game mode much more exciting.
