"#Threadiverse" - nice term. :)
On the technical side: I'm doing this toot from the Mastodon side. I used
https://MYINSTANCE/authorize_interaction?uri=LEMMYCOMMENTURL
where MYINSTANCE is the instance I'm on (https://framapiaf.org) and LEMMYCOMMENTURL is the comment I chose to reply to (https://lemmy.blahaj.zone/comment/90402).
If I understand federation correctly, my reply should/could turn up on the lemmy instances involved in the thread - even though I don't have a lemmy account.