Matrix is basically federated Discord based on an open standard. But it's a separate thing from the fediverse.

The thing is that Matrix and Discord are really intended for real time chatting, including private and encrypted chatting, in a way ActivityPub isn't (which is more about persistent public conversations). So it makes sense that they are separate things.

IRC

the problem isn’t Discord per se but that everyone insists on using a chatroom to replace support channels, wikis, knowledge-bases, FAQs, forums, announcements, mailing lists, etc.

I don't think we need to reinvent Matrix "just" to have some parts of it be based on ActivityPub.

It's being developed: https://github.com/MaddyUnderStars/shoot

IDK if that's a good idea, even Mastodon and Lemmy don't really interact that well. It's easier to just make a separate account for each type of platform.