What if there were a way to do this with multiple fediverse services?
What if you have an article, and the comments are 1 lemmy user, 1 mastodon user, 1 misskey user, 1 friendica user, ect ect ect?
Basically start making ANY fediverse service a viable way to leave a comment, which can be replied to by any other fediverse user, regardless of service?

That's just the base promise of ActivityPub, the basis of the fediverse. It's not a hypothetical, but rather reality.

That scenario you mentioned, it's not only Lemmy users that could reply there. All the ones you mentioned would have had access to that blog's comment section and been able to leave replies.

So if you have user@lemmy.world, and you go to his community, you see a thread, you comment.....your comment is now in the comments section of his blog.

That's just literally the same as me looking at this Lemmy thread from Mbin, leaving a comment, and it appearing on Lemmy.