In an interview with an Australian radio station, Arcade Fire’s Win Butler said that the music on the Her movie soundtrack will see an official release in some form. Here’s what Butler said about it:
We’re just slow as a band. The music will get out there, it’s just, like, a question of if we want to sell it to people or give to people or record other songs or whatever. There are many pieces on the soundtrack that are kind of based on actual songs that we’ve never really recorded. Yeah, there’s a song called Milk and Honey and a song called Dimensions that are, like, lost great Arcade Fire songs. They are actually just things that, like, fit the world of the movie and then we kind of wrote them to the film.
That’s good news! Here’s the whole interview (they start talking about Her at 15:40):