@scott Reminds me of the old 90-9-1 rule. 1% create content in a community, 9% interact with it, 90% just lurk. https://en.wikipedia.org/wiki/1%25_rule_(Internet_culture)
Because of the narrow target group of vis.social I hope as well that it will improve over time.
Maybe add a 1-month rule. If someone isn't active (Toot, new following, reply, etc.) for 1 month they get a notice per mail and have another month to become active. If not, their account is removed.