I have a publisher interested in some of my work, but they want it in their house style. They know about LilyPond, but it's "a fringe market they are watching" (their words). Their preference would be for me to submit in Finale or Sibelius, but I'm not interested in re-entering the entire score. I'm also not interested in spending way more than I'd ever make on the project to buy a copy of Finale (or Sibelius).
They have said that XML would also be okay.
And that's the history and reasoning for my question. My Google-fu unearthed a XML to Lilypond translator, but is there one that goes the other direction?