S3 storage pricing, for most users is just a rounding error compared to e.g egress or compute cost. And it has proven to be tremendously reliable, both in durability and access. No sane person would point a CDN against a Filecoin backed origin, right?
For kinda-censorship resistant distribution of stuff like Wikileak dumps we already have torrents right now, where the seeders are aware of the content they spread.
For uses where S3 is not competitive, like storage of my media rips, spinning rust at places like Hetzner exist, or Backblaze et. al for more casual backup uses.
The only point I can see for decentralised "storage" of this kind is for ultra high durability, small data size, almost never read, almost some sort of "stakes". One could imagine something like storing contracts/land deeds, similar to Gwern's timestamping of URL's. The files should be small, the storage model optimised for maximal durability (every node store's almost everything?), and prices high enough to ensure durability.
[0]: Just look at this PR page https://filecoin.io/store/ [1]: https://www.gwern.net/Timestamping