Certainly worth looking forward to
According to the information available in the game, the possibilities of getting an extra bonus is ability related with gears. There is no need of a base level for such ability, which means each level from 1 to 80 can get it.
But, we still have no idea if the new heirloom items will show up in Sword of the New World money or its expansion because we have not uncovered any of them yet. At the same time, it sure seems like Blizzard would not necessarily want Worgen and Goblin alts speeding past Cataclysm lowbie content. So, just because the bonus applies to 1-80 level does not mean the gear can be worn that whole time. But, the new change is certainly worth looking forward to.