Eh, it makes sense to have the 50 Anniversary in theaters. It makes far sense to make it a regular thing - especially not with the Christmas episode. Yes, Christmas is a busy time in theaters, but that should show you the kind of things Doctor Who would be up against in competition. A one time event in theaters is fun. If I'm spending my Christmas movie money, it's not going to be on Doctor Who. Also, I tend to avoid the theaters on Christmas day like the plague. First, I have other things to do. More importantly, the very fact that it's so busy means it's a nightmare to deal with parking, crowds, etc. If it's a one-day event like the anniversary, that means I'll be skipping it.
Just a bad idea all around.