Yes, it's one of those threads again. Hear me out though.
At the moment, there are basically two types of gameplay: healers and everyone else. For the latter, gameplay is "press the buttons in the right order as fast as you can". With the healer, it's "wait and watch for the opportune moments to use your abilities. So my idea would be to take that healer mentality of "wait and watch" and apply it to a tank.
And as it happens to be, Samurai works perfectly for that.
The cornerstone of the samurai's gameplay, much like the ammunition is for Machinist or switching between Astral/Umbral is for Black Mage, would be iaido. Iaido is the art of quickly drawing one's sword for combat. In manga/anime you see it used all the time, where an unsheathing, an attack, and a subsequent sheathing will happen faster than the eye can see. While this a tremendous otaku exaggeration of the traditional art, as Ninja has made concrete, Final Fantasy XIV is all about tremendous otaku exaggeration.
So Samurai would have two major stances: sword drawn and sword sheathed. These act similar to the other tank classes' basic defensive and offensive stances (e.g. Shield and Sword Oath) but with some slight twists. When the sword is drawn, enmity is increased and the samurai auto attacks. This will be the stance used to build hate and do standard attacks.
While the sword is sheathed however, damage taken is reduced, but the samurai does not auto attack, and most of their offensive abilities are locked. This is the phase for soaking up damage, but it is also the one where that core idea of "wait and watch" comes into play. Similar to Cyan in Final Fantasy VI, the Samurai would have a "charge" ability in the sheathed stance (and sure why not, let's name it "Bushido" just like Cyan's was). When this ability is activated, a numbered bar slowly progresses upwards. An attack wil be unleashed when Bushido is activated a second time, its type and power dependent on what number the bar reaches. The Samurai can do nothing else while this is charging, and perhaps should even move at walking speed, so therein lies the tactics: how long do you risk charging the ability? Obviously if you wait a long time you're going to get a bigger bang for your buck, but stuff could go to hell in the meantime.
While that would be the primary mechanic of the job, there would be others to cycle you back and forth between sword drawn and sword sheathed. For instance, a move I like the idea of would be a simple iaijutsu technique that charges the samurai forward, attacking enemies in its path while giving increased enmity. It would act as a good opening move, as well as one to quickly reposition oneself behind a monster. And it would look hella cool. The other abilities would be up for debate, though certainly staples from XI and before (Hasso, Third Eye, Seigan) would make it in in some form.
Oh, and the cross-classes would be Gladiator and Pugilist. It's gotta have Gladiator for Provoke (that ability is too engrained in every major fight to forgo), and Pugilist instead of Marauder because iaido, and samurai in general, fight with finesse, not recklessness.
Lemme know what you think!