my other idea was always to have Giselle show up. Just like in the movie, her prescence in the real world caused everyone to sing along with her. If in OUAT that was like a magical thing in her world, if she came to SB, there would be no curse necessary. Just her walking around and people being compelled to sing.
That or everyone just really wants to sing.
Eh, I get the impression that they are cautious about inserting live action Disney movies into OUAT. I think one of the biggest issues is that because those are live action films, people only imagine the original actors in those roles. I recall they even said once that they wouldn’t have Jack Sparrow unless he was played by Johnny Depp, aside from the fact that their version of Hook is obviously inspired by Sparrow.
Anyway, based on what we know, I think this episode will be their way of fully resolving the Evil Queen arc of the Season. It’s already been confirmed that she is appearing, and I get the impression that it won’t be just for flashbacks either.