However, this no longer seems to work on macOS Mojave (10.14.4)?
A possible solution is to install this Safari Extension:
However, I don’t have a Mac signing certificate to build it myself and I’m not sure I want to install a binary with an extension that can read all my web traffic.
I thought of using Keyboard Maestro (mapping Backspace to ⌘[ in Safari only), but can’t get it to work without breaking regular edit functionality in the URL field and forms…