I’ve always wondered how many people actually decide to use something like mastodon to see Lemmy posts. I mean I know how inadequate it can be with a lack of a proper UI but I’m just wondering. Especially, with the infinite possibilities this can have.
Considering that the vast majority of comments on every thread (including this thread) are from users on different instances than OP, I’m going to answer: “literally everyone on Lemmy, constantly, and on every post”.
It sounds like what you meant to ask was more about interoperability between different platforms, but keep in mind that even if other platforms didn’t exist, Lemmy would not be what it is without ActivityPub federation.