A different type of Cross-realm
How about instead of allowing players from all realms to join in arena teams, you restrict those from Lordaeron, since it is clearly a difference in gear from all sides, and it's not really fair for a low gs player from Lorda to be merged against a full bis war/ret, or any other class for that matter from Icecrown or Blackrock. Giving that we all know some of the player base uses "specail advantages" in arenas to gain the upper hand.
How about you allow cross realm joining in regards to dungeons instead?