Google is not cooperating with anyone when it comes to their existing proprietary E2EE implementation. E2EE is available in Google's client only, able to be run on the Android devices Google certifies, when talking through Google's RCS server.
That is because the core of their security model is a centralized key server, outside of the rest of RCS, that acts as the source of truth for an account and its associated public keys.
That fails once you have accounts which are not being authoritatively managed by Google, e.g. an email address with multiple messaging services attached, or a phone number which may be managed by any number of third party RCS installations. That is a problem which is still being actively solved.