In retrospect, the entire idea of a Sufjan Stevens Broadway musical feels both far-fetched and inevitable. Last year, director/choreographer Justin Peck and playwright Jackie Sibblies Drury’s Illinoise, an adaptation of Stevens’ 2005 classic Illinois, opened in Chicago. Last month, Illinoise came to New York. It’s currently running at the St. James Theatre, and it’s nominated for four Tonys, including Best Musical. Now, there’s an original cast recording on the way, and we get to hear two of its songs.