Small project is done in small steps. However it's nice to see how new primitives fit in together. This time I've added email notifications for myself to get alerted whenever a new user signs up / new stream gets created. I'm sure this can work for a long time before I'll have to disable new stream notifications first and new user notifications after that.
Fun fact: even with zero users, I already see bots probing the service in hope to find wp-admin.php
Also, user page was broken, due to template migration to new types, this is fixed now