Thinking more about how people could learn the game without YouTube or Tankspot, it seems that an Observer mode would be an excellent addition. Some mechanism which allowed you to join a fight in progress as a watcher only, hovering above god-style, kind of like you can hover around when dead and see what’s going on.
I’d love to be able to follow a Warrior tank who was running my chosen bête noire, to learn how they handle the adds and time their cooldowns. Or to hover over a new wing of Naxx once our guild ventures in for the second time. This would allow you to watch and learn fights that are new, or that you’re struggling with. It removes the element of surprise when encountering a new instance or boss, but then very few approach a new fight without first watching a strategy video or reading a debrief. In fact Observer mode would be much more involving than those kind of meta approaches.
You’d probably need some kind of way to allow or disallow observers, so as not to be encumbered with additional stresses or having strangers judge your skills. But given people Livestream their attempts already, I’m sure it would be a pretty popular feature. eSports depend on the ability for an audience to join a game as observers and hence participate in the event like they were at a real sports game. The venerable Quake engine allowed god mode overview for tournament play, Starcraft II will feature some kind of observer mode, as well as replays, so why not offer it in WoW too?