How exactly?
"This includes making messaging, voice-calling, and video-calling services interoperable with third-party services upon request" does not equal the death of encryption. No developer would ever do this anyway.
One, What's APP (or any services for that matter) would never want to do this because it would mean they'd have to create end-to-end encryption with iMessages thats different than their. They'll keep their loops closed. This is more about playing nice with other open standards like RCS. Two, if voice/video/chat app wanted to bastardize their encryption, they would likely be creating a separate channel for for Apple, and another for Google, plus their app-to-app protocols.... which again, NO ONE is doing that. You can also build bridges in between that translate back and forth... but no one is going to do that. The effort and development needed would be insanity and not have any return on investment.