This actually could be big, the problem is that it needs the same name recognition of a DropBox and Google Drive. Marketing seems like the most important part. Also it needs a way for the average user to use it the same way they use the others, with cash.
The minimal amount you can offer is 20GB, and even if you have exactly 20GB, you are not going to get any contract as you will have a very heavy penalization for low free storage (a multiplier in your score of 0.00024 in the case of 20Gb) ... I am sorry
Sia is not oriented to final costumers, but instead to enterprises and storage providers that want to use Sia as their storage layer instead of the servers of Amazon, Azure and so. Some services that accept FIAT an do all the Sia thing (exchange and protocol) in the background are being developed