However, they have made it so you must purchase them for gold. Here is a picture of the current prices for the heirlooms:
You can then purchase items that will upgrade these heirlooms to be effective to level 90.
Therefore, theoretically if you wanted every heirloom and every heirloom upgraded, it would cost you a monumental amount of gold, if the prices remain the same when the patch goes live.
Would you pay that kind of gold for all the heirlooms? Probably not. But, what if there was an achievement tied along with getting every heirloom? Or, even a mount?