I was confused. I thought chia was going to be also a storage mechanism. I was pointing out those coins that are built around the idea of storage.

That said, Filecoin does use some form of proof of storage:

https://filecoin.io/proof-of-replication.pdf

You need the proof of replication to show that a storage contact is being fufilled, not to secure the chain of blocks. proof of replication could be adapted to protect the chain, but that's not how it works at the moment. At least as far as I can tell.