I think this talk makes his opinion on how breaking changes in libraries should be handled (in the context of the JVM ecosystem) very clear:

A) avoid breaking API changes

B) if you have to do large breaking API changes, that will probably affect alot of dependent projects, make it a new artifact / namespace / library that can live side-by-side with the old version

B is actually pretty common in large java library projects (rxjava -> rxjava 2, retrofit -> retrofit 2, dagger -> dagger ‡ all have independent maven artifacts and I think also packages) and imho this approach makes a lot of sense. It's also the more important part of this talk compared to his critique of semver.