I believe we should drop IE11 support with the next major release. This would allow us to produce much more modern bundles.

As of June 2020 IE11 market share is only 1.4% according to https://gs.statcounter.com/

Users who really need to support IE11 would still be able to transpile our bundles or add required polyfills.

As part of this we can remove output.ecmaVersion: 5 from the webpack configs.