If you go to the main menu and go down to apps you can open the google play store and download it there! I came here to figure out how and then saw this and was disappointed but then went and played around and figured it out.
@nikonrachel Thanks for your idea submission. Disney+ is certainly an area of opportunity our content team had identified based on its popularity. So it is on our radar, but there isn't any news that we can share yet. Once we know more, we'll share it right here within this thread!