Think of it like this, you want to sell coins, setup a shopify store and sell the coin for USD at whatever price that you like. It could be any coin, bitcoin, litecoin, each coin is a product on the shopify store. buy the coin, provide your address and coins are sent to that address.
This is like an exchange that you're describing but it's just slower than the usual exchange that we have. If it's needed to provide the address for the bought coins to be sent later, that's a manual process, unlike the usual exchange that you can withdraw it anytime as long as you're at the threshold of minimum withdrawal.
What OP's idea is like the marketplace for e-commerce just like what we see with them selling goods and products online. But in his idea, it's his coins or any other coins that will be listed there.