But I doubt unleashing the full expressive power of SQL is the point here. It would easily turn a moderately complicated "remove column" migration a real maintenance hell.

In the simplest form, when you add a column to some schema, it should be materialized in the base schema and exposed via the migration view.

The problems start when you add and remove 20 columns because even though they are no longer visible in migration schemas, they take up space in the base schema