Currency for the new chest piece Heirlooms?

Zarhym on the US forums:

"One thing I can tell you is that chest piece heirlooms will be available in the next content patch. They will provide a 10% experience bonus that stacks with the shoulder bonus. "

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Ofcourse, nobody can name a price or amount yet, but I would like to know what SORT of currency can this chest be bought for?

- Is it Emblems of Heroism?
- Is it Argent Tournament Champion Seals?
- Is it Wintergrasp Marks of Honor?
- Is it Stone Keeper's Shards?

I would like to know what the currency is, so I can start saving that particular item, and not having to stack up on all 4 of them. Saves me a lot of effort!

Thanks in advance.