I know the main issue of the auction house was you didn't want them to flood the AH and essentially break it. My wife and I came up with an interesting idea that fits the lore. Here it is:

A Khaajit caravaneer likes to travel to the major capitals in hopes of finding a profit. He shows up twice a day to each capital (random hours) to sell goods he's acquired along the road.

how it works: There would be shout that would be zone wide of him being attacked by bandits. If you did not save him from the bandits, he would leave the zone and not return for 24 hours. if you did save him he will go to the capital and sell goods that he acquired or agreed to broker someone, for 1 hour real time. He would return sometime between 10-12 hours later. He would be just like how a merchant functions, taking out a small portion for his services. If you tried putting up items that he did not accept, he'd give you merchant value.

What he accepts: He would only accept tradeskill items, white traited items or world drop set piece items. He will not accept crafted items of green quality or higher as he does not want to risk being attacked for having high ticket items. He also would not accept any consumable items including recipes and motifs.

in essence, he allows the use to trade high demand items, without flooding the market. Given the variable of him showing up, you are unlikely to have everyone flood the merchant at once. Since he only lasts an hour the mega server would not be heavily taxed on a continuous loop. (such as it is for world of warcraft). Any thoughts? any flaws? lots of gripes i'm sure