Reactive damage is and has always been good for tanking... we've all begged that druid for Thorns, envied that paladin for Retribution Aura, and have a shield or two with a Shield Spike on it for multi-mob tanks. Now, not only do warrior tanks have their own reactive damage tanking ability (which, combined with the new Thunder Clap that has no upper limit on mobs it hits and Shockwave, the 51 point protection talent) but it scales with Strength/Block Value, meaning that as your gear improves you can select to increase this ability's damage and thus its threat. A mere 500 block value (trifling to attain with the new strength to block calculations) means you will deal 100 damage to anyone who strikes you or is blocked attacking you.
Even if (like me in the picture above) you throw on full DPS gear and don't have any active block value, your strength is going to add up to SBV in the 300's or above. That's more than three times as much damage as Thorns, it's always on, you never have to refresh it or ask anyone else to put it on you and it stacks with Thorns and a Shield Spike.
Honestly, what else is there to say? This is an amazing ability. If you are a tank, you should get this ability. In fact, protection spec warriors have absolutely no reason not to get this ability. It will be available as of Echoes of Doom, and if you intend to be specced prot as of tomorrow in the name of all the tanking gods get this talent. You're never going to regret more threat from a stat you're going to stack anyway.