Nobody is telling you to use it. This originally spun out of development of a messaging app just for Pixelfed, but evolved when the dev realized it could be made to work with any Fediverse account, not just his own server project.
An optimistic view is that it could end up opening the door for end-to-end encryption to come to private messages in Fediverse servers, over time.
I think what @[email protected] is trying to explain is that Mastodon and Lemmy for example may be able to implement Sup as a part of their softwares too. Currently if you try to DM someone on Lemmy, the options are a Matrix redirect, or Private Messages designated as not secured.
Though I do wonder about the viability of this. People would still need to set up with Sup to receive messages, at least as I understand it. As a result, this would run into a similar problem as matrix, just without needing to use a different federated server and login I suppose.
This would also require that project leads for AP softwares would want to accept the service as a part of their distribution, assuming it even is implmented in such a manner.
TL;DR it's hard to say anything for certain when details seem to be slim.
Yeah, my current guess for how this will work is that users will do an OAuth sign-in dance with their Fedi accounts to a client that is mostly not connected to their personal accounts in any meaningful way, beyond viewing contacts that have also signed in to the client. The client itself could store the encrypted chat, rather than having it reside on any server.
Eventually, we may be far enough along at a point that the ActivityPub protocol could have an enhancement proposal for supporting chat, and apps like Sup could plug into servers in a more native way, where the conversation data lives encrypted on the server.
This is all just conjecture on my part, but it seems like a viable way to work around current network limitations.
With the open nature of the fediverse I actually see some potential here. Right now there isn’t a single messenger that I truly like. They’re all just different shades of okay or worse.
Doesn‘t quite have the userbase at least for me. I‘m only using it for one work contact and that’s it. I also heard from others who use Element a bit more that it’s quite buggy, although I haven’t experienced that myself yet.
Signal is too darn secure. Much better to have one dude who probably knows how to use a crypto library build the whole thing over again with a coat of ActivityPub on top