At the same time, Google is in a tough spot here. The files and documents in your Google Drive (or Gmail) are incredibly sensitive. One possible solution is using the https://www.googleapis.com/auth/drive.file OAuth scope, which only lets you access files a user has explicitly shared with the app. I'm curious if iA Writer has limitations that makes this a bad user experience, but from a user security point of view, I can see why I want the apps that get to see my whole Google Drive audited too.
[1] https://developers.google.com/drive/api/guides/api-specific-...