Blizzard have confirmed that there will be no enforced CRZ in Pandaria. Blizzard Blue Rygarius has said the following in this post: “Please note that Pandaria zones will not have CRZ enabled when Mists of Pandaria is released, but players can group up cross-realm in Pandaria with Real ID or BattleTag friends. The Wandering Isle, the pandaren starting area, will also not have CRZ enabled at launch, though we’ll have multiple instances of this zone running as needed for each realm, in an attempt to prevent overcrowding.”
Players may still encounter people from other servers, as the cross-realm RealID grouping remains available, but no enforced CRZ will be enforced. If players encounter cross-realm groups, they are invited by others, not put there by Blizzard.
It is interesting to note that Blizzard anticipate heavy server loading and have therefore taken the approach of instancing the pandaren start area – the Wandering Isle. This small, densely populated area with its tightly packed quests could be a hotbed of overcrowding issues, so it will be interesting to see how Blizzard’s approach plays out.