I understand some restrictions, especially all of them relating to gold (1 million gold, more or less pocket change in 2019, would make you the kingpin of the AH, the Rockfeller of coarse stone, the Gould of arcane crystal).
Still, maybe the restrictions could be airtight one way. For instance, doing the War of the Shifting Sands questline on vanilla give you the mount in vanilla and in retail ?