Here’s the gist of my idea so far:

stores (or alliances of stores in similar industries) :: instances

inventory items :: posts

counts :: votes

item categories (or entire stores depend on implementation) :: communities

moderators are only allowed to post items to their own community or instance.

comments can still exist (perhaps as item reviews with the same upvote/downvote mechanic).

No actual transactions would be processed over this protocol. It would be solely for inventory broadcast/aggregation (like Shopify in that it houses the inventory of many vendors except without the transaction ability built-in since pub-sub is horrible for that kind of thing).

Edit: if you have any opinions (even “what a stupid idea!”) I’d be open to them. I haven’t even written a single line of code yet and it’s a fresh idea in my head waiting to be shot down by someone less idealistic than myself.