By the time The Flash and Supergirl have their next crossover, the Maid of Might will already have met Professor Martin Stein and the rest of the crew of the Waverider in Invasion!, December's massive, four-show event.
Could Stein, then, make the move to sharing some screentime with Supergirl and The Flash in their musical crossover near the end of the year?
It's hard not to wonder; while the "Flarrowverse" is replete with musical talent ranging from Jesse L. Martin and Grant Gustin to Melissa Benoist and Jeremy Jordan, it's Garber who has probably sung the most onscreen for Berlanti.
Already this season on DC's Legends of Tomorrow, Garber had to keep Nazi agents from suspecting his team's undercover operation by impersonating Hitler's favorite opera singer -- and that's just the latest instance, given that Garber appeared on Eli Stone, a series from Berlanti and Arrow and Legends showrunner Marc Guggenheim that dealt with a lawyer whose brain tumor was causing him to hallucinate elaborate musical numbers.
"Oh, I'd be crazy not to," Berlanti told ComicBook.com during an interview at a party celebrating Arrow's hundredth episode. "He's got one of the best voices. He actually sang for me at an event once, and if I ever get married, I'd have him sing at the wedding."
That seems pretty definitive, although with Garber as a series regular on another show and no clear idea of what the musical crossover will entail yet, it leaves open the possibility that Berlanti will do the "crazy" thing, for one of any number of reasons.
So far, all that audiences know is that a crossover between Supergirl and The Flash will happen. It will take place near the end of the season and will not be connected to the four-show Invasion! crossover.
There has been speculation that Neil Patrick Harris could be cast as the Music Meister, his villainous character from the musical episode of Batman: The Brave and the Bold, but that's at this point nothing more than hopeful guesswork on the part of fans and the press.
DC's Legends of Tomorrow airs Thursday nights at 8 p.m. ET/PT on The CW