For a good portion of the 9 million people that play this game, most time is spent in the upper echelon of the leveling process. Grinding out the early levels plays out fairly quickly, and with the upcoming changes that will make leveling easier, even less time will be spent in the lower brackets. So how does Bliz, a company that has always wanted their subscribers to appreciate their work, keep people from skipping the huge majority of content in an effort to hit Outland (and Northrend) asap?
The answer is simple. Customize old-world instances with options for high level content. It wouldn't be too difficult, I imagine. We are currently experiencing just that sort of thing with the Headless Horseman settled inside the Scarlet Monastery Graveyard. And while it is a short-term addition, there is no reason why Bliz couldn't introduce encounters of that kind all over Azeroth and in a more permanent fashion. And players dig that kind of thing, especially when there are good incentives involved. Sure, the 5-minute epics were nice and all, but more importantly, the encounter and social environment it created was FUN. Remember the huge crowds that waited just outside the SMGY portal? Players flocked to take part in the event, and stayed for the carnage. It was definitely a good time.
There is a lot of potential with the Headless Horseman event model that I think could work very well. Of course, having a multiply repeatable, epic-dropping quest doesn't really fit in with Bliz's intent to have us "work" for our gear, but if the mixed things up a bit, it could definitely work in the long-term. Say, what about adding boss encounters that required a 10-man raid, and having such bosses drop raid gear (ala Onyxia)? With the one week cooldown on introductory raid instances like Karazhan, I'm sure guilds would love the opportunity to give their members more than a couple shots at Tier gear -- and this could be one way they could do it.
Another approach would be to simply convert an entire old-world raid instance to a 10-man or even 25-man Level 70 dungeon. Bliz is warm to the idea, having serious plans for putting a rehashed Naxx for Level 80s into the next expansion. Now just do the same for ZG, AQ, MC, and things will be looking up for Azeroth.
What's old is old. But what's old that's new, well, that's just pure sweetness. =)