Tank role actions: Rampart, Low Blow, Provoke, Interject, Reprisal, Arm's Length, Shirk.
Extensively used in all/nearly all EX/savage/ultimate fights: Rampart, Provoke, Reprisal, Arm's Length, Shirk
Used rarely in specific savage fights: Interject
Never used outside of casual content (because lolbossimmunetocc): Low Blow
Almost every single piece of the tank role actions sees extensive, regular, use. Now personally, ever since the change to Interject in ShB I've been a very vocal proponent of SE making more use of the skill in EX/savage/ultimate. Even though it was a minor thing I quite liked the bit in E1S adds phase where each tank had to interrupt their specific add's cast of Mana Boost in order to prevent the following cast of Mana Surge from wiping the entire party with a raidwide blast. Perhaps my liking of interrupts has to do with the fact that I played SWTOR before FFXIV, and interrupting of specific skills in PvP in that game was a very important thing, but I do feel that it's an under-utilized mechanic that could have at least a little bit more potential from a mechanical perspective in fights. As for Cover, well, if SE were to make it a tank role action with something like a 90 or 120s CD then I think some sort of mechanic where a tankbuster gets targeted on a DPS or healer, rather than the tank, forcing one of the tanks (or both if two of them go out) to identify the target it was going on and Cover them to mitigate it would be neat. I can see that wiping pugs in savage constantly though.