This largely depends on the kind of software system you are working on. These sorts of DDL migrations are common on the kinds of Rails apps I’ve worked on over my career. Size of the table, traffic patterns, who uses associated features, tolerance for small downtime windows, or orchestrating a multi-phase zero-downtime migration are all ways to justify these migrations, and is preferable to alternatives that would be comparably over-engineered for that app’s business and technical context.