Yeah, I totally agree here. There is an optimal size. Three people commenting on one post might be too limited, but 10k people commenting on one post is pointless. There's a middle ground that will be awesome. Also, maybe the slightly more decentralized nature of a federated setup will solve that problem entirely? I can foresee places that do become Reddit size, with islands of tiny intimate communities that preserve the smaller feel that people seem to be enjoying today. Only time will tell!