As a store owner with both an in-world store and a MP store, I'd like a system that would allow me to set inventory levels of an item in the MP listing, and have that tied to an in-world object as well. That way when a person visits my MP store and purchases, say, an item I only am selling 10 of like a limited edition artwork/print, if someone goes to my in-world store they now only see 9 available. If that visitor buys it in-world, later visitors to my MP and in-world store only see 8 now available.

At the moment, you can not tie the two together, and for anyone selling only a single copy of an object, you have to sell it via the MP and then, once sold, go in-world and remove it and indicate it was sold. You can not show it and sell it on the MP if it's also available in-world for sale since if it's bought in-world, it still shows as one available in the MP.

This is obviously only applicable to sellers who deal with limited quantities of goods and want to maintain both in-world stores to show the item, and also a MP presence.