'Experience: The amount of experience needed to gain a level has been decreased between levels 20 and 60. In addition, the amount of experience granted by quests has been increased between levels 30 and 60. '
Since this is a balance issue it should be in the game upon release, just like how we already use 2.4 talents.
Another example would be this, it was also implemented during patch 2.3:
'Vendor Discounts: All vendors with an associate faction now give discounts at all levels above neutral.
Friendly: 5% discount
Honored: 10% discount
Revered: 15% discount
Exalted: 20% discount
Quest givers who have available daily quests will have a blue exclamation point instead of a yellow one. '
I don't suppose we will have to wait until patch 2.3 before we can get the reputation mechanics, so it doesn't make sense to wait until patch 2.3 to get the updated EXP mechanics.