I have actually considered trying to play two characters completely independently of each other and may try it once I hit 70. The idea would be to have the left half of the keyboard setup for character A and the right half of the keyboard setup for character B and try to play them separately with their own movement, action buttons, etc.

I am a big proponent of using the mouse for movement because you get a better response time for many things but I may be willing to give that up in order to play two characters at 90% utilization. In fact, the only way I would multi-box PvP was if I could control all characters individually with 80%+ utilization and even then it would be for BGs only, not Arenas.