Based on Harris’ comments, it would appear the actor hasn’t officially been contacted by The CW to potentially appear in the Supergirl and The Flash crossover.
It’s possible that Berlanti and those involved with The Flash and Supergirl musical episode held off on making announcements so as not to distract fans from the Heroes vs. Aliens crossover.
Of course, The CW only recently aired the four-part crossover featuring heroes from Supergirl, The Flash, Arrow, and Legends of Tomorrow — which proved to be a ratings powerhouse for the network.
That said, The Flash and Supergirl’s musical crossover is expected to air sometime in February 2017 and, as such, will likely film at some point in January.