I wonder if it would even be technically possible to get the St.John concert in full HD
I don't see why not. If the TV Show Star Trek: TNG can be finally released after 25 years in HD, I don't see why it can't be done here. It's expensive and time consuming (it has to be done shot by shot), so you know that's not happening for anything Mariah related.
I think by re-do she means another round of Christmas stuff, since she does this every year.