Fediverse

To be fair, Matrix is not exactly trying to be a "discord alternative" so much as an "all messaging platforms alternative", but it's still embarrassing that this feature is not present yet. It's been heavily requested by the discord crowd for years, and should have been a higher priority.

As for friends switching, at least Matrix has bridges and puppeting/double-puppeting support. Unfortunately, I don't think discord voice channel bridging/puppeting will ever work, so it's really not that useful in this instance. I know ripcord has voice channel interop so it is technically possible, but it's probably too hacky/abusive to put in officially, and it would probably only work with puppeting.