Maybe 10 years from now if this picks up. Reddit did not have as much on its first days either.

I wonder how federated activity pub instances fair on seo

Given lemmy is federated it's probably going to be significantly harder to search. I'd imagine if you went looking for "lemmy" content you'd be a lot more likely to get lemmy.world or lemmy.ml rather than sh.itjust.works or beehaw content for example, since those have "lemmy" in the domain name.

Yeah this is one of the main uses for Reddit.

It might be harder with Lemmy instances spread across different domains, but hopefully the search engines learn to prioritize Lemmy well

If the user base and content continue to grow at the current rate, it’s very likely. Reddit won’t just go away though. There is still a lot of content there and most people won’t stop using it anyway.

Depends on SEO and ActivityPub. I could see a dystopian future where the Silicon Valley refuses to improve on this use case, to push monolithic social media forward, which would also be in the interest of authoritarian governments.