How would that fit into a movement tier? If the Water Elemental was a talent in that tier, you'd be stupid not to take it. It would be a straight up dps increase. It just wouldn't work. I would be pretty pissed personally if I was FORCED to have a Water Elemental, even if I was Fire or Arcane.
Also, inb4 changing it to Arcane Familiar or Phoenix for the other specs.