Hopefully never, honestly.
Reddit was at its best 10 years ago, when it was still kind of a small niche subculture. Not big enough for the media to mine for content, not big enough for corporations and celebrity PR people to bother manipulating. And yeah, I realize this isn't super inclusive, but needing to have a modicum of tech savvy to get in the door was a great filter on the culture and content.
It was... how do I put this... far more SILLY, but far less DUMB than today. As the community grew and became normie-dominant, every thread became so predictable. So bound by the exact same patterns and conventions, the mindlessly referencing old references to farm karma, etc.
- "Unpopular opinion, but ."
- "I'm going to get downvoted into oblivion for this, but ."
- "I hate sand, it's coarse and gets everywhere." ... "From my point of view, the Jedi are evil!"... "Well then you are lost!"... <insert 10 more reply levels deep>
There was a lot of ugliness in the old Reddit. That comes from the hardcore libertarian "free speech" ethos that dominated the overall Internet back in the 2000's. I'm not too worried about that today, because the overall culture is just far less libertarian than it was 20 years ago. You DO need active moderation to avoid becoming 4chan, but I think an Internet community is more fun before the English majors show up and take over, and everything becomes performative hang-wringing about how how problematic everything is.
Also, I feel like if and when the normies get here, the "federated" aspect will fall away. Look, there's just NOT going to be hundreds or thousands of Lemmy instances that all have duplicated meme, movie, Star Trek, etc communities. The crowds are going to push toward consolidation, and a small number of instances are going to "win". Maybe just a single one. Right back where you started at that point.
So yeah, I think that the fediverse is far too small today, and needs a lot more activity in order to be self-sustaining. But I'm FINE with it reaching a self-sustaining critical mass, and then hanging out in "techie niche" territory indefinitely while Reddit keeps the casuals.