I think Bittorrent could be made usable for 1:1 transfers. The building blocks are there. But you'd have to streamline the process and build a client optimized for that case instead of the more common usage. The main missing piece would be a standardized encryption format. That doesn't really need protocol changes, just a storage-level convention how the data is encrypted before turning it into a torrent.
I really wish magic wormhole worked conveniently on windows without obliging me to install python and pip and such. It's my go-to when sftp isn't an option, but for sftp not to be an option almost always means that one of the computers I'm trying to transfer between is a windows box.
Wormhole requirement: "the URL of a publicly-available Rendezvous Server"
This means its not a self-sovereign system, like Bittorrent, GIT, and Bitcoin. Its no different then a central Napster server, the one that got dragged into court on November 1999. Scientists are still working on creating self-sovereign peer-to-peer systems. Its hard, but we're going to solve it in coming years.
Scientific community: "International Workshop series on Distributed Infrastructure for Common Good", https://dicg2020.github.io/ (disclaimer: involved scientist)
First time I hear about Magic Whatever™. Any modern download tool needs to be embedded into browsers and mobile OSes for it to have any chance these days.
I haven't seen any regular user use a separate download tool or a download manager for a decade or more.
Except for BitTorrent clients, but those aren't targeted at 1:1, of course :-)
Webtorrent is not fully decentralized since webrtc needs signalling servers for each session (you can't even store credentials in a cache and reuse them later) and it doesn't have a DHT since UDP isn't available in browsers.
Agreed, but I don't think there's a lot of motivation to do so. At that point, BitTorrent is just DCC in a new fur coat. As stated earlier, BT is most appropriately used in a setting where you want to download a single file from multiple sources, distributing the workload between them and your network. This results in faster downloads, and does so in a way that is decentralized (for the most part) and scalable by design.
So while it could be done, the question is really "should it be done"? I'd love to be able to send a file over the internet easily without using some centralized service, but if there's only 2 people that are meant to have the file, does the overhead of BitTorrent make any sense?