For those of your unaware, the armory bonus enables you to level alt jobs faster in Final Fantasy XIV - up to the highest level of your highest level job. So if you have a job at 75 all alt jobs will receive bonus experience up to that level.
I believe that WoW should add something similar to leveling. When we have one character at maximum level that has finished the campaign all subsequent characters leveled on the account should receive a 50% experience increase while leveling.