I don't really understand what is going on here, but I do know it's not the first time the all-musical format has been tried on a series. One episode of "Buffy, the Vampire Slayer" was all done in song (the result of a demonic spell cast on the characters) and it worked!

The ability to comunicate effectively only in song does have some dramatic yet realist utility when used as a result of some mental trauma. IOW, its not inconceivable something like this might actually happen in real life, due to an physical or mental injury.

There's a story Joey Bishop used to tell about his early days in Vegas, when he shared a dressing room with Country Singer Mel Tillis. Tillis had a severe stutter which went away completely when he was singing.

According to Bishop, he came to his dressing room one night to find Tillis in a state of hysterics, so excited and upset he could not communicate at all. Bishop, finally giving up trying to make sense of Tillis' ravings, shouted out in frustration "Sing it!"

Tillis sang back, clearly and melodious,
"We've been robbed!"

Someone had broken into their dressing room and stolen their valuables.