I think a site like Reddit can't easily be federated. It bills itself as the "front page of the internet" because it's an aggregator for people to find interesting topics. If you distribute this, there will be many "front pages", which makes the whole "aggregator" concept nonsensical.
And having one Reddit clone as the new "front page" where people use federation only to comment on that site seems to defy federation, too.
Reddit will be succeeded by another centralized service.