The ability to open your own shop with your loot and goods you crafted is what makes the game even greater. I would love that.
It would develop real economy to the game and help buy/sell item more often then shouting all the time in world chat.
There is no need to pay anything to open shop. It is kinda ridiculous. the idea of paying in AH is that you post an item for 2-3 days and can go do whatever you want. But here you actually have to go afk because you lock your character.
One more thing. People should not be able to open shops all aroud the town whereever they pleased too. Usualy it end like 100 ppl is vendoring in one place. First you cant go through because instead of clicking the ground you click someones vendor's bubble/characher. Second, its chaos all aroud and while checking shops you dont remember do you already check that one or not.
So what i suggest is to make a vendor district in towns where players can open they shops, or better idea allow players to open shops along sidewalks only next to each other. That way people always can walk freely through streets without problem and by the way check what is to buy. No chaos, nice trading system, no awful AH.