In order to have permanent pets such as Unstable Familiar, Clannfear, Twilight, and Bear to single bar slotting some changes need to be made to make this viable while also introducing some complications more than just freeing up two action slots and one ultimate. They would have to remove the effect of them being indefinitely summoned by making them duration based, not a big issue they would probably have an extended duration of 10-15 minutes or up to 30-60 minutes is not a problem. They could even add a refreshing duration effect when using their special ability so they don't expire during combat or at unforeseen circumstances.

What would be the problem is that every time you move into an instanced area or change zones you will have to recast the spell to summon them every time; I think that's a reasonable trade off. The other issue I can really see come up is with Werewolf transformation having access to 3-4 pets, even if their active special would not be available with action bar restrictions, you still have more combat bodies by your side. Then of course how much of a power increase would it be if you freed up 1 ultimate or 2 action bar slots, having the Bear around with Northern Storm could be a fairly large damage boost, but how much of a boost could it be?