Rust would be a good fit, yes, but many other languages could be a more comfortable fit. For example since we're just doing a simple data processing task, a simple language like Go would work perfectly. Since the realtime constraints are not super strict, you can build fine BT clients in comfortable languages such as C# or Java as well.

An advantage of Rust however is that it's easy to expose a C api from it, so it can easily be integrated into a project done in a more comfortable language.

>a bittorrent that actually does more than download and quit always seems like something quite heavy...

Don't forget to seed!

Let's brainstorm ways to solve the seeders/leechers problem via cryptocurrency: how much would it cost to encode a complete feature-length film in the bitcoin blockchain? :P

Bram Cohen built MojoNation which was the first real cryptotoken/smartcontract startup

After that failed he designed BitTorrent to actually align the incentives of users, without any of the currency bullshit getting in the way

The user would torrent a scrambled file, once some conditions were met the user would receive the mechanism for unscrambling the file. While the user is seeding the scrambled file they would have an alternate metadata that describes that file. The version that is served could be based on consensus of the network.

a solution already exists. it's called a private tracker.

Seems like having every single full node storing multi-gigabyte files for the few who actually want them wouldn't go over too well.

It does seem like a good fit, yes. Just for example, rtorrent regularly crashes every few days.

Security is the main gain for many people.