The MP draining thing would make it too much like DRK and then DRK/WAR would even need more DPS to keep there roles as the more damaging tank because that is the main focus of PLD is to be more defence then offence and the Zeal effect shields blocking Magical is also slipping into DRK area. All in all this sounds too much like a change to PLD. But none of them are terrible ideas and it's something you could make a new class on.