This idea is great in thought, but how do you plan to moderate the hoards of spam that will constantly be jirating through the /l chat?
Let me tell you about free for all link pages and free Classified ad websites (having started a couple myself in the past). The people who visit them are people who are advertising, not necessarily people who are looking for something.
You're trying to provide an alternative to something that is already easily accessible, efficient and convinient for both the buyer and the seller. The time it takes for you to spam the linkshell, find a buyer, select a meeting spot, go to this spot, and conduct the trade... is probably comparable to the time it takes to go to town and buy/sell on the auction house.
That aside, I think the fatal flaw would be how widespread you would be distributing these pearls... assuming your plan was to get everyone on shiva... you will have to have hoards of pearlsack holders. If someone is kicked out of the linkshell for spamming it like mad, they could easily get back in... especially if they have a friend who is a sack holder (because you can't see who invites who to the best of my knowledge).
I don't know, it could work, prove me wrong... but I'm just being proactive.