In my opinion an Auto-Attack would totally destroy the battle system of FFXIV.
It would make the usage of the stamina system and it also would make it much harder to attack the monster on certain spots to make your skill effective.

like. you stand behind the monster - want to activate skill that only affects the head - you move around the monster but the auto attack stops you like every step so it takes you forever to get around this monster.
its a definitive NO GO from my side