Agreed. While I admit that this is unlikely to happen, I think it would be amazing. The addition of the "Jeuno Marketplace" or "Ru'Something Bazaar" might be fun, would ensure they were connected to /yell (if they were part of regional Jeuno), and might be able to assist in the meeting of buyer and seller.
Imagine a simple but attractive zone, textured and detailed similar to the Jeuno zones we have now, that is largely an open area - perhaps with some fountains, planters and trees for appearance and immersion - that has categories listed on the in-game map.
A "commons" could be in the center, for sellers with mixed inventories or who are less motivated to use the map's areas, with in-setting descriptions for gear, spawn-items, synthesis items, etc., located in various places on the map. That way, buyers and sellers could locate by business type to combat the model limit that plagues a pile of sellers in one spot.
Obviously I am being very general and vague, but I think it would not only be a fun way to combat the problems addressed in this thread, but also a way for the community to self-filter the process to match buyers with just the bazaars selling what they might be looking for. Incentive to use this kind of zone could be found in a reinstatement of the general Jeuno tax (perhaps even a stronger one) that does not apply in the "sanctioned marketplace."
Is it likely to happen? Perhaps not. But it is fun to dream.