Good point about niches; I'm already a fan of SCOT tribes because they are helping in terms of creating interest groups and making content discovery a little easier.
I'll be interesting to see how SMTs/Hives impact the Steemosphere; I'm hoping a healthy level of granularity ensues... not too "generic" and not so specific that we end up with a bunch of semi-stale tribes with 7 members, because they are too tightly defined. I suppose we can but hope that the user base the natural intelligence needed to figure it out.
=^..^=
I think there will be communities that could have many thousands, others that have very few members in a very tight niche. As long as they are valuable to the users, it doesn't matter much.