I'd say Leona's A Moment Like This could fall into that category too. Most viewers probably hadn't heard it before or realised that it was Kelly Clarkson's winning song on American Idol 4 years previously (she launched in the UK with Miss Independent).

 

I don't think the 2014 winners single being a largely unknown song will necessarily be an offputting factor, perhaps it could be an advantage because it'll seem fresh? I assume a fair chunk of the X Factor viewers probably weren't aware of the likes of Hallelujah, When We Collide, Cannonball or Impossible either. These were all slightly more left field choices than Against All Odds, When You Believe etc.

Apparently the 2014 Winner's Single will be the OneRepublic Single from 2013 - 'Something I Need'.

It was not released in the UK or USA, but it was a Top 10 Hit in Australia & New Zealand.

 

OneRepublic's version may enter the top 40 next week as every other original version of the winners song has

Wonder if using this unreleased track is a down payment for getting Ryan Tedder on board to write for the winner's album.