What do you mean with “replacing”?
Example, I’m not visiting reddit anymore, instead spending some of my social media time here on Lemmy. So for me it has already replaced it.
But if you mean replacing reddit as “the Internet’s frontpage”. I don’t know. It would be nice, but on the other hand, maybe we shouldn’t want that.
Nope, it really doesn’t need that, just use any of the web clients if you need that.
But lemmy, nor Mastodon, nor Pixelfed, nor kbin need that.