I agree with the OP. Now that Movies Anywhere allows you to have a single library across the major digital distribution services - it would be awesome if I could access that library from Plex too so I had access to all my movie content in one place.
Pro-tip: it looks like if you link your ultraviolet account with vudu (for the free digital copies that come with many dvds and blurays) and then link your vudu account with Movies Anywhere, you get access to all your ultraviolet movies even in services that previously didn’t support it (like Google Play and iTunes)