Answer by idleberg for activate soft wrap (at preferred line length) for specific file types only?

You can override the global soft wrap settings in a package's settings:

1. Open your Atom settings
2. Click on Installed Packages
3. Search for language-text and click on the package
4. Edit the soft wrap settings

If you feel at home editing your config.cson, here's a minimum example that reflects this setting:

"*":  editor: {}".plain.text":  editor:    softWrap: true    softWrapAtPreferredLineLength: true