Before today, I could ask Google Home (and, in turn, the Google Assistant) to play streaming programs such as Netflix and Hulu, but not with Google's own Play Movies service.
Everything that changes today, you can now ask Google Home to help your TV show or watch movies without linking accounts, after all, you're using the Google Assistant to access another Google service, as well that all is attached to your account. This also applies to rented or purchased movies or TV content.
In fact, the new functionality is so close that you will not even find a configuration for Play Movies within the Google Assistant settings, which kind of makes sense.