No, I'm talking about developing for those users. Right now if you want to write the simplest, dependency lightest export code that those users can double-click

No, I'm talking about developing for those users. Right now if you want to write the simplest, dependency lightest export code that those users can double-click and open in Excel you are writing yet another CSV export. It would be nice if instead you could take an existing API that returns JSON and wrap it in a mimetype like application/json+excel, and add a Content-Disposition: attachment; filename=thisapi.xljson and get Excel double-click support without another flaky CSV file.