I've absolutely adored the few musicals I've seen, but it's not because I find the idea of a whole crowd of people breaking into song as being particularly plausible. I certainly never played FFVI thinking it was unrealistic how all the characters could talk by conjuring up giant text boxes.

That said, as much as I'd adore a Final Fantasy musical, I do wonder how well SE would handle that sort of thing if they tried to make it work as a game. I would love it if they adapted the story or world of a Final Fantasy game into a musical, though.