This game still can't even give a consistently rock-solid indicator of when an enemy's AoE attack will hit. Whether an attack hits you or not is still calculated well before the animation actually occurs, often creating absurd scenarios where your corpse lies well outside of the blast radius. Full-blown action combat with attacks striking precise areas in real time is completely out of the question.

But technical concerns aside, I don't even find the question to be valid. You can't just plunk action combat into an MMORPG with traditional tab-targeting, with all the content designed and balanced under that system. It just doesn't work that way. You are basically asking to change the whole genre of the game and alter the mechanics at their core -- might as well be trying to make FFXIV into a 2D side-scrolling platformer.

That said, before FFXIV came out I was actually hoping it would lean more towards a somewhat action-based style. Maybe something like Guild Wars 2, where attacks and projectiles move and strike in real time, but you can still "target" things. But that would have been a very different sort of game, not anything like the FFXIV we know today. Maybe the next Final Fantasy MMO, if there is one, could experiment with this -- but not this game.