I'm learning how to tank on my druid (one raid needs a tank or they can't raid), and I so want the following...
Basic Tank Training: this would be a series of quests you'd be required to do before you queue as tank. You'd get teleported to a series of rooms. First off you'd either be able to talk to an NPC about the basics of tanking as your class (aka, a warrior uses a sword and shield. They use the following abilities to keep the mobs on them (thundershock, whatever else they use), and are in defensive stance. They like mail/plate gear with defense and whatever else warriors like) or skip the intro and jump into the first trial. All basic trials would have a NPC healer to keep you up, and who can pull healing aggro.
First trial: hold a boss mob's attention. You don't have to move. You would have a threat meter and you'd need to get it above a certain point in a certain amount of time.
Second trial: hold a boss's attention while periodically needing to move out of bad stuff.
Third trial: get and hold a trash pack of mobs. First group is all melee, second has a ranged/caster.
Just a very quick intro to tanking. You could always go back and redo any trial, even if you passed. The idea would be that experienced tanks could breeze through these in a few minutes, but that novice tanks would learn stuff.
Intermediate Tank Training:
Similar setup, but now we include NPC DPS. You'd repeat trial 2, then do trial 3 twice, once with suggested crowd control and once where you chose the NPC DPS group and tell them what to cc. Again, all trials can be repeated, so you can really experiment with different group makeups and crowd control options.
My guess would be that Advanced Tank Training would involve trigger-happy dps, tanking cooldowns, and switching tanks. Doing all three questlines would get you something, like a shield vanity pet or the title Tank.
I would kill to have this stuff in game, especially the ability to practice! DPS get target dummies, why can't tanks have practice scenarios?