It seems a lot of the arguments for or against an 'auction house' are based on convenience and time. I have an idea of how we could have both of them in a very good working system.
I was totally for an auction house when the game was released. Without the search function the market wards were a complete disaster. I honestly think that buying in ffxiv's marketplace is a lot more convenient now. I have not had trouble buying anything from the marketplace in a long time and honestly, if all I had to do was buy things I would be totally happy and loving the marketplace right now. It's like an auction house with 20 seconds of delay more or a bit more. It is different and perhaps a recycled idea but in a way refreshing and immersive. The only problem comes when you have to sell something or pick up your gil. Then it gets too complicated and bothersome to the point that I rather vendor or sometimes even just TOSS everything to save time. It takes too long to sell that I think some people can't be bothered and this is the biggest problem that I see with the marketplace.
The idea of the retainer selling your things does not have to be deleted or erased. It can still be that way. They can make it so that you can still have retainers but instead of all of them cramped in a dark damp zombie house they could populate the streets of Eorzea. They could be summoned anywhere in the world. in the camps, or the streets of UL'dah, Gridania or Lima Lominsa or outside in the wilderness.. but at the same time give them some idle animations etc. so they dont look like dead zombies crowding the world. They could add an auction house/broker/bidding house basically a "buy/sell/collect gil" interface. Then you can have both retainers selling things for you at popular gathering places like camps and cities or by NM's or instance dungeons, grinding locations etc while you have your central trading interface selling things and where you can buy things quicker and more conviniently!
This would give people the central trading/buying/selling/collecting gil interface they are looking for (where they can buy/sell and pick up gil all in just a few minutes and so encouraging the economy of the game as well) and at the same time you would still have a perfect use for your retainers who could seek items for you, sell or repair your gear even while you are out somewhere doing something else.
All of a sudden crafters would be much happier because there would be more materials in the 'central trading house' and buyers would be happy cause that would mean more things to buy and more gil to spend. And you would still have your retainers giving the empty lands of Eorzea more life. It would be like you can AFK bazaar all the time... but you don't have to be logged in for that and you don't have to be running your game or standing there afk. (this is what I imagined when I read about the game before the it's release.)
I also think price history is really unnessecary if something like a 'central trading house' would be added. I think at all times there would be enough of one item for everyone to get the best price for them or have a reference to know how much to sell it for. Also some materials could be cheaper or more expensive, easier or even more difficult to obtain today than tomorrow or next month. It's not fair for people to base there opinion of what an item is worth based on what someone else paid for it last week or last month. The prices should not be carved in stone but based on availability, supply and demand. That means it's alright for things to be cheap if there is too many of them for sale and a price history should be irrelevant. At the same time it's alright for things to be more expensive (if someone just went on a buying spree and bought all the dodo hides available for example, then they would cost more till the supply got high enough to drive the prices down again).
There should not be a problem of knowing what is a good price for most items as most of the time there will be should be some up (since it would be so convenient to sell buy or pick up your money) that everyone would almost always have a reference for prices. For the most rare items you have to agree that no price history is necessary or fair. If it is a rare item you pay for it if you think it is worth what the person is selling it for not weather its an affordable good fair price. If it is a rare item it means if you want it you buy it now for whatever it sells or you might have to wait another month for another opportunity to even have the chance to consider weather or not you want to pay XXX for the item.