Wouldn't your approach be 100% covered by current type implementation ? As a workflow, if every time you create a new spreadsheet you first define all the colu

Wouldn't your approach be 100% covered by current type implementation ? As a workflow, if every time you create a new spreadsheet you first define all the column types and constraints, you're in the world you're describing. Passing around that spreadsheet would also keep these settings as long as it's not converted and everyone's version is compatible. That means you get the best of both worlds: people who care about strict types can be as strict as they want, other people can benefit from auto conversions.