Google Maps joined the Google App as having an official beta version this afternoon, and you can sign-up now!
All you need to do is hit that link below, click the “Become a tester” button, and then head to Google Play to “update” to the beta version. It’s just like you have done with the Google App and Nova and any other beta through the Play store. That same link below will allow you to leave the beta test as well.
The new beta version is 9.27.0.
Google Maps Beta Sign-up