Why Proof of Work? Shouldn't everyone switch to Proof of Capacity or something else?
Proof of Capacity (aka Proof of Space) suffers from the same exact problems as GPU mining: it’s commodity hardware, and there’s a lot of it out there that could be used to 51% attack the Sia network. Further, if the coin price goes down, the miners wouldn’t care because they can just sell their hardware on the Sia network, or on Ebay, and they will still be able to use it for profit.
Other solutions, like Proof of Stake, are inherently insecure and/or not ready at this point in time.