Leveling is becoming a more daunting task with each expansion, and this is bad for the game. People can complain about 'just add water' characters and claim that people need to be 'committed to putting the time in' (and seriously, dokhidamo, your signature says you're a 'permanent ex-WoW player' because of tri-spec? hilarious.), but the fact is this attitude just doesn't cut it. As the bar to entry becomes higher, while the game gets older, fewer new players will come in to replace the older players who are going out and the game will stagnate. Forcing players to play through 7 years of outdated content just so they can run with their friends is poor design, and I completely expect Blizz to add some kind of mechanism to alleviate this at least somewhat.
I think a good solution would be to make the leveling process quicker (much as they have with each new expansion) but also introduce a quick path up via scenarios. For example the path to 60 for a human character could begin like this -
1-10: The scenario begins in Elwynn forest where you are trained in the basics of your class. You are tasked with meeting 3 sparring partners - each who instructs you on the use of a primary class ability. After you've completed this 3 objectives, a final objective pops up - defend goldshire from Hogger and his Gnolls! You clear 3 waves of Gnolls and then face hogger, who requires proper use of the abilities you've recently trained to defeat him. Upon completion of the scenario, you are instantly leveled to level 10.
10-20: The scenario begins in Lakeshire, currently under assault by Blackrock Orcs. The player meets 3 NPCs - a tank a healer and a DPS - which explain a bit about each role and then offer to join the player. If the player is in a tank spec, the DPS and Healer NPC join him/her., etc. They then face several waves of Blackrock Orcs that have abilities that must be dealt with appropriately by that role (example, a tank spec player must keep aggro off of the DPS and Healer and also kick an important ability. A Healer character must keep the tank character up and dispel harmful effects from the DPS, etc.) Upon completion, you are instantly leveled to level 20.
This could go on and on, but the idea is that, through this set of solo scenarios (that can be quicker than leveling, but can also be tuned to not be 'easy') you are given a crash course in your class and also the basics of the game. Rewards for completion could be a set of non-DEable, non-sellable green gear comparable to quest greens for that level range. This could last to level 60, or all the way up to 85.