See background at https://github.com/netlify/team-dev/issues/36

Once #494 is done and released, we should use pure ES modules and make a major release.

This is more than just switching from CommonJS to import/export. See this list for other changes which might be involved. This should be broken in many PRs, as much as possible, to lower the risk. Also, non-breaking changes (such as adding file extensions in imports, or loading JSON files differently) should be done before the breaking changes (such as using import/export statements).

This should only be done after pure ES modules are supported in both Netlify CLI (netlify/cli#3514) and Netlify Build (netlify/build#3742).