Divine Veil and Stoneskin are really the only two compelling reasons why PLD might actually want copious amounts of Vitality. Stoneskin's function gives it good parity with high Vitality if the PLD can cast it on themselves, as its effectiveness scales directly with the target's HP. Divine Veil is similar, because the shield given to the party is based on the casting PLD's HP.

Unfortunately, there isn't enough need for tanks to generate that extra mitigation in the current paradigm, so Vit tanking is still only for stubborn folks (or people idealistically hoping 3.2 will change things).