Yes things have changed a lot on YouTube since this was first posted. I think Youtube came up with a brilliant way to benefit all parties.
However, if someone's going to put a Christmas cover song out somewhere other than Youtube it might still be wise to shell out the bucks for a license or stick with the public domain songs unless the new model is across whatever platform site they're intending to use.
That is 100% correct Josie. As far as I know content Id is only for YouTube right now so for other digital platforms you still need to purchase a license for copyrighted material.
Of course there are still some copyright owners who are being sticky about YouTube and will demand that your video be taken down but I think these are very few and far between. Even they are beginning to see the light that it is a win win suitation.