Since we all play together anyways, would it be possible to allow it for Blackrock/Lord/Icecrown people to form groups for Instanced pvp and be in teams together? Sort of like on retail. Maybe create a "global - PVP" channel that would allow it. Wouldnt have to actually interact server wise with the person from the other realms bar forming a team somehow. Only meetups taking place in instanced pvp.
Would make finding partners a lot easier and would breathe more Life into the pvp scene of the non blackrock servers. Even on icecrown (not to speak of Lord) it can be difficult to find a person to play with at certain times.
I see no real drawbacks and a lot of good could come of it.