I have trouble finding a space on my hotbar for Shirk. It'd be nice but I just can see giving up:

Convalescence (OP when used with Clemency and/or Requiescat self-sustain)
Awareness (You can't block a criitcal hit. On PLD this makes Bulwark and Passage of Arms much stronger.)
Reprisal, Rampart, and Provoke are forever slots.

I'd give up Awareness and take Shirk if you aren't a Paladin. Though I've never had a problem Tank swapping.