So Ferrel wants to bring back the grind and make leveling slower again, while Chris thinks leveling should be slowed down by giving less xp for quests. Both talk about how much better life was in Everquest, where most players never even reached the level cap (I didn't), and how MMORPGs should be about the journey, not about the destination. But I think both of them simply missed the real purpose of the end-game: It enables people to play together.
Take for example the blogging community guild Single Abstract Noun. We had a lot of fun when we started, posting "guild first" screenshots of Ragefire Chasm. But the longer the guild goes on, the thinner we are stretched over the level range. Some people already had level 80 on that server, some created level 55 Death Knights, and all the others that made new characters are now already covering a wide range from level 1 to 30. I logged on last night to see if I could find a guild group, but while there were a lot of people online, there weren't 4 others around my level (20) with whom I could have gone to the Deadmines or Wailing Caverns.
Take any group of friends, and chances are they have the same problem. Unless they create specific characters who only ever play when doing things together, people tend to drift apart in levels, because they play different amounts of time and at different levels of efficiency. But given how long one expansion lasts in World of Warcraft, and how fast you can reach the level cap, the group of friends is likely to find themselves back together at the level cap. Doing heroics together at level 80, even at different levels of gear, makes a lot more sense than a level 60 player grouping with a level 30 player.
Thus, if you want to change World of Warcraft or another MMORPG to slower leveling, it isn't sufficient to just reduce the leveling speed. You also need to enable people to play together in spite of level differences. Systems like in City of Heroes, where people can temporarily lower or increase their level to that of their friends in a group could work here. If you don't have such a system, slowing down leveling only prevents people from playing with their friends for a longer time, and that is never going to be popular.