Everytime I read something about SemVer, breaking changes, etc, I can't help but think about how well Symfony (the PHP framework) handles this.

With Symfony, major version changes are not there to break things or bring in tons of new stuff. Instead, it just removes BC layers for stuff that has previously been working but deprecated (with appropriate deprecation warnings).

This makes it easy to switch to a new major version: simply fix all deprecated calls and upgrade, done. At least that's what I experienced moving a project from Symfony 2.x to Symfony 3.x.