You can guess the answer from healers' responses which usually summarized as only healing without doing anything special is boring.

For me it would really depend on the fight itself. If the raid is going to be something similar to what we have then I won't even bother playing tanks. However, if the battle system for tanks also got changed by adding for instance parry similar to assassin creed in which you can throw the balance of opponents or twisting their arms and deliver a hit (block+atk) I think it would be more awesome and more enjoyable.

Though lets face it. We won't have a major change to how battles are executed since it will shatter the core of the game and it would be more realistically to implement a new game for such new battle engines.