Thanks to @Thib support for #XMPP URIs got merged into mastodon a few days ago. This should make linking to external discussion channels and moving a conversation to a E2E encrypted chat a bit easier on the fediverse:
https://github.com/tootsuite/mastodon/issues/9776
@nipos @rra requiring a space before and after would break things like mentioning with a coma immediately instead, which I think is quite frequent. Having a colon right after a handle might be less common, but I think it's common too.
In the end, I think those two handle formats are in the end too close to do anything meaningful with it :/