Risk / reward for a tank sounds tricky because you're not just risking your own neck, you're risking everyone who you're protecting. As much as I like the idea of a high adrenaline tank who needs to live on the edge, I think a safety net still needs to be in place where a low enough threshold of HP means a higher buff for... damage, defense, healing received? Something.
Considering the size of the weapon, I certainly hope they've got more AoE potential than PLD.