Board Thread:Spoilers!/@comment-27060727-20170222030619/@comment-27060727-20170301201259

I'm going to bet that while the musical episode as a whole will not be a dream or alternate world, I still don't think it'll be part of the actual conscious plot. That will be the other 21 minutes of the episode. The title itself suggests inner reflection. I imagine one of the scenes could go like:

Snow to David: "Remember our crazy wedding day?" Regina: "How could I forget." *cuts to reflective dream scenario in which the wedding is dramatically re-enacted through song*

And since they are pretty much promoting this as the last season of OUAT as we've known it for 6 seasons, these musical scenes could also be their alternative to an actual retrospective clip episode.