I think this is the answer.

Lemmy and (maybe) Mastodon (I don't know enough about it) will be the inspiration for something that goes mainstream - but I do think that they'll be the Myspace to the next big things Facebook - Perfect for people who know how to take advantage of it and it will be a mild success because of it; but someone will come along, streamline and spruce it up and that will be the new standard