Spooncraft

This is obviously undocumented and not official in any way, just take this information at face value.

Mr. Badass himself, Boubouille, at mmo-champions they found this little change form patch 2.3 to 2.4 regarding experience needed to hit level 70 and some possible leads into how experience will work for the expansion: Wrath of the Lich King. Blizzard has stated though that they are increasing the amount of experienced gained in Outland dungeons and from group quests.

It looks like a change went unnoticed on the 2.4 PTRs, Blizzard changed the XP required to level up at … 70 ! Before the patch players needed 814,700 XP to level to 71, but since tuesday you need about 50% more xp to reach this level, bringing the total to 1,256,500 XP. According to a few reports this change was made because of an interface bug but increasing the max xp by 50k or 100k would have been enough to fix it, this leaves us with another theory : leveling in WotLK will require 50% more xp than what you needed in BC, it wouldn’t be surprising and would be equal to the same difference of XP between Burning Crusade and WoW classic.