The more this trick will be used, the higher the cost of the dedicated fast internet connections with cloud hosts will become. Most people buying dedicated, unlimited uplinks don't upload the amounts mentioned in this article, which is why bandwidth is relatively affordable. If everyone buys into this network to make a profit, the prices would probably rise to the point that profit drops. This isn't against any kind of ToS I know of.
The "make 2.4x your investment" promise also assumes your server will actually serve 100TB of content. The more people join, the fewer files your server will serve and the less profit you'll make.
In the end, the system is profitable until the network has reached the size where everyone breaks even. If people leave the network, profits go up again, if people join the network, profits drop and people back out. People renting servers game the system trying to one-up each other and in return Farba gets a worldwide CDN for cheap.
The best trick may perhaps be that server providers may directly buy into the system, as they can get bandwidth and servers for lower margins than their customers. This gets Farba high-quality service for cheap while the service providers add a relatively easy income stream on the side.
All of this comes at an additional cost to the customers, because now your battery-starved mobile phone is validating cryptographic signatures of images and other content.
This also leaves legal questions: who's responsible for illegal content hosted on servers hooked into this network? If your hosting provider of choice gets a takedown notice for child porn or malware, will you still be able to use their services?