They implemented something called CRZ's (Cross Realm Zones).

Similar to when you're in a battlegrounds, where someone's name has an asterisk next to it indicating they're from another server.
Basically, everywhere except the main cities (or maybe there too, not positive on that), if a zone is not populated enough you get players from more than one server.

The idea being, none of the zones are dead.
And in the case of a PvP server, the sides will be roughly equal in numbers at least.

You're in a zone with people from the same region type: PvP, PvE or Roleplaying servers.