If the Dominion met with the Vorlon of Babylon 5, or the Borg met up with
the Shadows as well, on Babylon 5.
Imagine if Londo Mollari and Weyoun had a very long, intense conversation, ha.
I also like HRH's idea, the crew of Firefly arriving on DS9.
"It might not be so bad. For all we know the Vorta could be gluttonous, alcoholic sex maniacs."
~Quark and Ziyal