It's a nice idea in theory but in practicality it is very sucky when you generally play one side of the faction. Examples include:
Having to level the adorable moonkin twice to 25.
Having to level a toon to earn the rep and etc to buy those stupid guild pages.
That dimwitted child/pet from Argent crusade that somehow can't battle yet is still caged up near the menagerie like an animal.
Trust me you don't want it.