The fact that mastodon apparently doesn't scale well could be a feature rather than a bug. You probably don't want thousands of users on a single server, since that brings with it all sorts of problems - social, technical, economic.
@bob I've thought about this as well: might be an excellent way to stop the global echo-chamber: If ideas propagate first in communities of interest, then go broad perhaps thought-bubbles turn into foam of thought. More individual bubbles means more different ideas.