I see a lot of people here making the mistake of thinking that IPFS is a file storage system that splits up content among a decentralized, shared network when it's not.
If I have a file and "store" it on IPFS - that file sits on my own machine indefinitely. You would think that a project called “Interplanetary File System” would be able to store some data... but nope. Instead, files in IPFS are only ever distributed to other hosts if they express interest in that content, and they are mirrored only if their clients have been setup to seed that content.

IPFS in that sense is more like Bittorrent in that it doesn't magically guarantee data will be available. That is the reason why you see so many “decentralized” systems using IPFS that suck. Because the moment data is “stored” in Interplanetary “File System”, the user thinks they can close the application and the data will still be there.... Guess why there are so many stores on OpenBazaar that are inaccessible at the moment ;)

The reason why so many Ethereum developers are using IPFS is because these developers typically have no clue what they're doing. They're the kind of developers whose introduction to blockchains came in the form of an artificially-imposed toy sandpit and now they think that blockchain engineering consists of being able to build towers out of blocks built by other people. They cannot build anything new for themselves, and if they understood how any of the existing components worked they probably wouldn't use them... But they don't.

After doing some tests, IPFS seems to run their own caching servers that automatically cache content retrieved from the network via their servers. So I am guessing that “dapp developers” are “optimizing” their code to use these servers, or are making requests to these servers in tests and then assuming that IPFS is a magic data store that gives them infinite decentralized, scalable storage space for no cost.... I mean, economically that is already impossible. But even if it could technically do that, ask yourself what Filecoin is suppose to be for?

On the topic of Filecoin, it's a complete disaster and the paper linked in the OP doesn't cover any of the main technical problems. What this paper fails to address is how unreliable time-lock encryption is as a timing function for anything given that its impossible to know how much serial computational power an attacker has available. That already defeats most of the claims made around Filecoin's absurdly inefficient and impossible to verify “proof-of-spacetime” algorithm.

The other thing that none of these papers addresses is how an auction market is fundamentally at odds to the needs of a cryptoeconomic system. The problem is that with no way to regulate the supply of storage space, it naturally leads to more people wanting to sell what they have then there is demand for it (which will crash the price of the storage space.)

If hosts cannot remain profitable by playing fairly then the only option left is to cheat. This is actually the opposite to how blockchains work as they strictly control the supply to maintain a healthy security-cost ratio (technically there is only ever 1 Bitcoin whose scarcity is maintained via a growing proof-of-work. The “bit” comes from the virtually fragmented sub-coins, but there is only ever 1 Bitcoin.)

Tl; dr: Interplanetary File System can only do distribution and cannot actually store files; And Filecoin isn't really a coin at all since the supply is indeterminate and it functions more like an exchange for contracts than a currency. The Protocol Lab guys sure know how to bullshit people though, I'll give them that much.