This completely ruins how I used the Music app. In the iOS 9 Music app, you could build a queue using "Up Next" and "Add to Queue". This way, you could specify a song you wanted to play next and then songs that you wanted to follow that song before returning to the normal list of songs (whether that be on shuffle, a playlist, or an album). Now, "Play Later" doesn't build a queue and instead just shoves songs at the bottom of the list, which totally isn't how this feature is supposed to function and no other music app implements it like this. Spotify and Google Play Music both do this correctly, I don't understand how Apple expects to compete when it ruins its own features with every major update.
EDIT: Also, I just checked and this feature works as it did in iOS 9 on the newest version of iTunes on Sierra, so I'm wondering why iOS 10 and iTunes 12 have the same "Play Later" feature but they work in completely different ways.