One of the biggest benefits of Amazon IMO is it’s homogeny. That is, It’s ability to let you buy products from dozens of different categories, among thousands of vendors, with a unified shopping experience. For any competitor to replicate this would be a monumental task and it would probably take years to see profit. I think most of us want to see decentralization of retail and increased competition and the best way might be a decentralized shopping platform.
While not something that can easily be shoehorned into the Fediverse I think it’s worth the effort to try. Sensitive info like addresses, order history, and payments would still have to be managed outside of the Fediverse, but I think it is feasible to have a federated platform that makes it easier to connect consumers with retailers.
Now that I think about it the idea is closer to eBay. I just had it in mind to disrupt the biggest online retailer without simply reimplementing their model. Also, the centralized nature of both means they have much more influence. If instances are federated it should be easier, for retailers and consumers, to switch if one guy to be too influential or charged too many fees (I assume instances would get some kind of kickback). Like someone else said, you can think of it like a mall but imagine if you could relocate your shop from one mall to another in a matter of days or even hours.