Lovely, but there's little Plex can do.
Without legal talks, the current model of Plex Cloud may collapse at some point in the (distant) future since it relies on Amazon's services too much. However, the Plex Cloud user base is worldwide while Amazon's content has its restrictions and relatively narrow target audience.
Furthermore, I don't see who's gonna be the pushing force in this potential legal battle. Just look at Netflix: they are legally presented in a whopping number of 190 countries, and yet suffer from content availability issues, namely localized content (subtitles/dubbing). It's okay for anglophone users, but not so much for the rest of the world.
Amazon's cool with it for now, since it creates a niche of long-term Amazon Drive customers with lots of identical content in the cloud. Then again, Amazon isn't the only cloud provider our there.