Reddit, in my opinion, has become mainstream due to its ability to be searched via engines such as Google. I think Lemmy would need to have that same level of discoverability if the platform should take off. I'm not sure if doing this risks Google or others threatening the platform via "embrace, extend, and extinguish", but perhaps Lemmy needs to be accompanied by a decentralized search engine itself that can browse the entire Fediverse. I'm new to the fediverse so I'm not sure if such a software exists, but clearly I think discoverability is paramount for giving new users a reason to see Lemmy and maybe stick around
If Lemmy gets big enough, google will work on any customized scraping of the fediverse they need to add in, because it'll be in their best interest. They might already be able to since Lemmy isn't private for non-logged in users.
In fact as a user of one different forum I was able to witness search engines logging in as bots for better access. I know this sounds made-up, but the forum was made with/powered by Xenforo. Btw XDA forums and lot of other forums are also made with xenforo. It's possible that xenforo has a built-in support for search indexing bots, but I don't reaľly know if that's the case.