IMO the main problem is the mainstream use of NATs and the fact that most people don't run their computers 24/7. The internet became the internat.

If all computers were publicly reachable it would be trivial to send files peer-to-peer.

I guess IPFS can be an interesting solution to this problem.

With the advent of smartphones, most people are running a computer 24/7. But that computer is still either behind a NAT or on a connection where data is precious.

NAT punching is a thing, but it makes the implementation of p2p a lot more complicated.

UPnP was supposed to help with this as well before it became a security disaster. There's also stuff like https://github.com/danoctavian/bluntly/blob/master/README.md to do NAT holepunching without a central server (using DHT) but again adoption and the actual ergonomics of usage (npm, the config file, key distribution etc make it fail the "could my grandma use it" test) are not easy enough to make it easy enough for the un-devops'd masses.

Some crypto currency based on file backup (say, Sia or Diskcoin) could completely solve this problem since you could just drop a magnet link to some encrypted files to your friend and your file stays accessible for as long as your funds cover it.

Pretty much.

The world got paranoid, as any exposed port to the raw net is seen as an invite to worms.

NAT and port blocking are orthogonal, getting one with the other is mostly a coincidence.

> If all computers were publicly reachable it would be trivial to send files peer-to-peer.

WebRTC exists today, and it's quite good. It's not a technology problem, it's a matter of practicality. Mobile devices being reachable over the network 24/7 is just not realistic (connectivity falls off, battery considerations, etc.). I don't want my phone to heat up and come to a crawl because the video I just shared is being downloaded by three friends over LTE while I ride the train.

I think it is more an IPv4 problem -- everyone is fire-walled and NAT'd up the wazoo and direct connection require some UDP + voodoo (or at least it did last time I investigated this).

a UI problem and a legal problem. It's difficult to create a service that is accessible to people who barely understand what a file is, and won't be taken over by pirates and then shut down by law enforcement.

The fact that files can only be downloaded once from this new service isn't just a coincidence.

I agree that it's a sort of UI problem. I could be sharing a desktop with a customer with Teamviewer (which maybe has file sharing, and it's telling I'm unsure about it) and at the same time talking with him on Skype, which for voice is still good (it's bad for everything else - text, files, screen sharing - video calls are of very limited use.) But I can't easily send a file to the other guy.

Unfortunately AFAIK there has been no successful open point to point file transfer protocol that different OSes could implement and be interoperable over the Internet. Going to https://send.firefox.com/ and drop a file there is not an improvement. It's still centralized. Is there any solution to the problem of discovering the address of the sender and the recipient without a central server? I would think it's an impossible problem but there are clever people out there. Maybe mesh networks?

You can send files (and retrieve them) with Teamviewer, but it's unbearably slow most of the time.

I'd venture to guess it's more of a copyright and monetization problem than a UI problem.

Indeed, I remember when a "pair of netcats" was the preferred file transfer solution, and even for IM "meetings". Almost no one knows what I'm talking about if I mention it to most people now, even those otherwise experienced in computer use and/or are developers themselves.

On a similar token, there still isn't any good attempt at a user-friendly E2E-encrypted email solution that integrates with what people already use (minus a few PGP-based browser extensions which don't have much adoption yet).

old chat programs e.g. Trillion did this just fine.