I love A7X but I must admit I don't really think that it'll be made ever unless they come out with two more albums then maybe. While they have been around for 11 years or so I don't think that's enough time. Also like Ohioman said the difficulty would be around nightmare-like difficulty (again no pun) for drums and guitar. I'm fine with them just releasing DLC as I'll buy pretty much all of it.
But you never truly know. A lot of the times when I go to play band multi online people only have a few downloaded songs and most of the time it's A7X so it's probably selling well.
