Some niche communities are lacking, though I don’t see them existing/growing without a large increase in userbase, since they’re you know, niche. Cities for instance… some I used to frequent on reddit exist on Lemmy, but are naturally not as active. Also I used to talk in (hooray) a couple subs about chronic illnesses which are like, 1% or less of the population, maybe more since sometimes it would be family members or parents talking. Celiac, type 1 diabetes. Same as cities there are communities about those but they are not very active yet.