I spent a considerable time by introducing conditional user defaults (making it possible for one user preference to have different default values based on eg. user registration time, thus allowing us to save considerable amount of database space). I'd like to write the blog post, covering the journey and describing the issues I ran into during the work.

Relevant task: T354459: [Epic] Support conditional defaults for user properties to help address user_properties table bloat and subtasks

Draft is not available ATM; filling this task early to capture the idea. Might be best completed once T357072: Echo: Drop droppable rows from user_properties gets done, so the space difference can be measured & included in the post.