> it's hard to see how paying people to host your stuff on their own machines can ever be cost-competitive with paying AWS to do it

That's a big part of Amazon's AWS offerings, hosting other people's files on their own machines. Heck, Amazon could spin up IPFS host nodes and start earning filecoin for themselves. The goal is that file hosting becomes competitive, cheaper and more available. You won't have to choose AWS or DigitalOcean, you just throw some change at it and anybody can host it.