This is promising. I like the idea and it has real world utility. In the world of cloud storage though, what benefits would users have using decentralised storage? P2P like torrent already presents some form of meaningful 'storage' already, and is ubiquitous technology.
Sia is very torrent-like, in that you can download from multiple peers simultaneously. The difference is the introduction of cryptocurrency. If you squint, you can view Sia as a means of incentivizing people to "seed" your "torrents." The reason no one stores their personal data on a torrent is that there's no guarantee that people will seed it. The closest we have is private trackers with "seeding points", "upload credit", etc. Sia gives you much stronger guarantees that people will retain your data, and better ways to manage the risk associated with P2P cloud storage (e.g. encryption, erasure coding).
So I accumulate the Sia through apportioning some of my space to the network storage quota which if used rewards me with Sia.