I would love to see NPCs that players can place and stock with items for sale, similar to how player-owned shops were in Ultima Online and the player-owned vending machines in Rust. Of course this would require some kind of money system (maybe even banks with bankers to store your money that could be built/placed by admins).
This would enable players to sell items to other players even when they're not online, make villages more active centers of commerce, and add another fun element to the game. Players could set the prices for their items and other players could interact with the NPC through an interface similar to the trading to browse items and buy.
This would also promote player activity more than if it were just non-player-owned NPCs that you had to sell items to, and create a more dynamic economy, especially as more items are added such as cooking and baking. Players could create their own shops such as bakeries, blacksmiths, carpenter, tailor, etc.