I think this is a great change. I am not a fan of heirlooms. One of the elements of leveling that I really enjoy is upgrading gear and watching your character's visuals change. But the XP bonus made heirlooms too advantageous.
This way, the people who don't want to upgrade gear can use heirlooms, while others can avoid them. Or maybe only use them for trinkets or weapons, if that's important enough.
I hope Blizzard does not add any other bonuses, and just makes them very optional.
Blizzard should also take the opportunity to simplify the heirloom system. Right now there's a complex series of upgrades with different prices and different sources in order to increase the maximum level of the heirloom item. It would be best if the concept of upgrading heirlooms was just removed entirely. All heirlooms simply scale to the max level before the expansion. When a new expansion is released, all heirlooms have their caps increased simultaneously.