I see a use case for signing messages. It could be like the Twitter verification for public messages.

For encryption, as in only a few users can decrypt the message, I can’t see it. Like “Sharing personal information with friends”, why do you want to do that on a public channel? Use a private messaging system, or the section inside the service you use.

Because there isn’t a viable solution for this that I know of that is asynchronous and. Things like Signal, Session, iMessages, etc are “instant messaging” and are synchronous.

The use-case would be more similar to dropping some files on a web server, password protecting it and linking to that in a Twt.