It is very likely that World of Warcraft will further raise the level cap in future expansions. Maybe not in all of them, but I doubt that level 70 will remain the cap forever. Raising the level cap is usually popular, because it allows everyone who is stuck at the current cap to easily increase the power of his existing character. But the disadvantage is that if you ever want to change character, getting back up to the level cap gets longer and longer. Ask the people that for some reason made a new blood elf or draenei, for example to play a Horde paladin or Alliance shaman, and you'll see that most of them leveled to 70 in a hurry, not enjoying the process very much. Shouldn't there be a shortcut?
Some time ago Dark Age of Camelot introduced a /level command to their game, with which somebody who had already leveled at least one character to the level cap could simply skip to level 20 or even 30 with an alt. In World of Warcraft you could think of a /level command that brings you up to level 50, thus skipping the most boring levels you would otherwise have to spend in Stranglethorn Vale, but still gives you character 10 levels to play in the old world and 10 in the new Outland, to get used to his new character before starting to raid.
The advantage of opening up a quicker route to level 70 would be that the more level 70 alts a players have, the easier it is to form a group with the right class mix. Instead of the current situation with far too many hunters in the game, just because these are most pleasant to solo level, people could more easily make a character of one of the classes that is more needed for a group or raid. Of course that would be completely optional, so if somebody likes to level up, or for example first play the first 20 levels in the new starting zones, he is free to do so. But for somebody who has already seen certain zones far too often and doesn't want to do the same quests again, skipping the part he doesn't want to play should be a possibility.
On the other hand that would a rather cheap shortcut. I would rather have that Blizzard in the next expansion introduced new zones for all levels, so that anyone who wants to level up an alt can do so with completely new quests and zones. That would be more fun for people who aren't particularly keen on the end-game too. But of course that would require a lot more work from Blizzard, and right now I'm a bit pessimistic about whether they are ever going to create more low-level content. So at least a /level command would help.