An astral shard economy maybe.
But any chance of a widespread plat economy is pretty dead due to the ease of getting plat at higher levels and the inherent caps in place (character and AH).
Even at my slow ass pace, making half a million plat over a weekend just from vendor trashing what I loot out of epic quests is about the norm. That's ~1/8th the character cap as a side effect of general playing over a weekend. Actually farming would be better. How can any sort of trade economy ever compete with that? What sort of prices would need be set to make it even worth the effort to deal with the AH UI?