Website perezhilton.com reports that Sia is after all included in Madonna's new album, out in spring. It's a strings and flutes song co-written by Sia and produced by William Orbit. It's probably called "Trust", as previously reported.
Also, the album will have four ballads and apparently Martin Solveig and Stuart Price have both done some remixing to "Gimme All Your Luvin".

 Stay tuned for more details!