> files could be broken up into shards and distributed across multiple nodes
You can setup any old distributed database to do this... If there was a benefit to breaking down a file rather than replicating it, AWS would be using this efficiency to provide a better service.
> the effect that a commoditized pricing system would have on the costs of a distributed storage solution
It'll always be cheaper for someone to sell their hard drive than to sell access to their hard drive, just like it is cheaper to buy bitcoin instead of mining it.
Here is why: let's say Alice is profit-driven and greedy and is making $1 profit for 1gb of space. She can use those profits to buy more hardware, make more profit, buy more hardware, and so on and so forth until she has 100,000gb of space being offered. At that point, because of economies of scale, it will cost Alice less to maintain 100,000gb then the total cost of 100,000 people hosting 1gb each (eg. reduce total electricity cost because of bulk purchase).
Now, Alice can grow her operation so big (say, 100 petabytes) that it actually becomes no longer profitable for Bob to host 1gb. Alice has so much lower costs per gb that she was able to drive the price per gb down to a point where the price is lower than Bob's costs.
This is basic economy of scale so far, right? And it's the same reason why data centers filled with ASICs make it useless for you to mine Bitcoin on your laptop.
OK now that Alice is hosting say 100petabytes and has priced out all the individuals on the network, she will be subject to data policy rules and will have to obey law enforcement to kick out users that are using her hard drives for illegal activity.
Alice is now AWS.