It could actually work. It would be perfect for those two to perform it in the UK (maybe as the fourth single or so, during the holiday season, at the XF, or at the 2014 BRITs). It would cause controversy becuase of the Diana reference but Gaga wouldn't really receive backlash because of the Elton feature. Plus, the song is amazing and it's pretty obvious that it will be on the album, since she's doing with it the same thing she did with Y&I.
How do you not want Gaga to collaborate with Elton?

If she played it well, that might take her career to a whole new level, especially in the UK.