I would rather suggest to remove Shirk instead of the tank stance. Shirk has no purpose anymore, now that Provoke gives additional enmity and tank stance has no damage penalty. There is no need to dump your enmity anymore when you tank swap.

Turning on tank stance at the start of a duty really is not a problem and much less cumbersome than pressing Shirk every few seconds, especially since Shirk needs a target. So annyoing targeting or macro-queue issues.

I really see no benefit here. At all.