The services I think is best suited for federation next in my opinion is Stack Overflow / Stack Exchange. It’s a site aimed at programmers, so a larger percentage of the target userbase cares about FOSS and open standards. It has shit tons of moderation problems which SO is trying to solve by democratizing itself to some extent via meta stack exchange and the SO elections and surveys, but true democratization by letting people hosts their own instances of SO seems infintely superior to their attempts. Being able to have different SO instances cater towards different audiances, a more beginner friendly SO, an SO that really wants to avoid redundant questions, etc. Also having a way in which multiple different qa sites can talk to each other would make finding solutions so much easier. IDK it seems like such a no brainer to me.