I like the idea of personal bazaars, like in FFXI (a merchant class might be fun). That way everyone could have their "sell single" option, without bothering the bulk sellers on the Market Board. Sellers would just have to find the right location to provide their wares. I always wondered how well it might work if sellers could make themselves available in locations without the Market Board (Dragonhead, Mor Dhona, etc).

A custom Quest board would be nice too, where players could set up their own quests and rewards. Fun times