The bag is currently available on the Patch 3.3 PTR, and given the official WoW Twitter account's tweet earlier in the evening about it, it looks to be here to stay once the patch hits.
Of course, the reason question isn't who's going to buy these -- anybody who's already bought a mammoth and a motorcycle is who. The real question is, who's gonna start selling these for 5k on the Auction House and hope people don't catch on?
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to the Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.