I think I might be alone in this, but I personally don’t want a musical episode unless (unless!!) it is written, directed, and totally under the supervision and vision of Joss Whedon. Like, A and E take a week long vacation to Borneo and Joss just pops in on a whim and manages to write and shoot a musical episode.
Also, it has to air before A and E come back from vacay and change things.
I could see them getting Alan Menken and Glen Slater on board. Considering the show’s heavy association with Disney, they would make the most sense from a business point of view. Not like they haven’t done TV before, either. Rest in peace, Galavant. I imagine one of the biggest hurdles is whether enough cast members are capable of singing well. Off the top of my head, the only current regular cast member I know of with musical experience is Colin. For everyone else, would they be able to successfully coach them? One reason The Flash and Supergirl are getting a musical crossover is because they realized that quite a few of their actors have a musical theatre background.