I would be surprised if they do explain "Calypso", but in "Facing the Strange" they did touch on it, and I'm guessing that Zora wondering if she was having another "dream" will serve as the explanation for the "Calypso" story. I think they could've went to the "Calypso" future, but they didn't. Granted, there was only so much time in that episode, but I'm guessing if they were going to address it directly that was a good time to do it.