Depends on what the view of “mainstream” is. With Threads, Tumblr, Discourse looking to join the Fediverse within a years time it’s going to grow by millions. It’s annoying when people use “algorithms” the Fediverse has algorithms. They are simply a tool. Awesome thing is that if any platform becomes hyper aggressive and looking to monetise users data there are ways to cut them off and there are other platforms and clients to use. Showing people interesting posts isn’t harmful, it’s done on the Fedi currently. Anyways, I believe adding millions more is good enough. It doesn’t need to be 100s of millions of active users