Sure, SOME older songs would need to be altered quite a bit in order to be played, but you mustn't forget that others would be much easier to make work. I'm betting that "In The Mood" would be incredibly easy to play with lower vocals. I'm not saying that that song SHOULD be played, I'm just saying it COULD be played. Sure, "Bastille Day" would need to be reworked, but who knows? They might surprise us and get some songs working that we'd never thought were possible anymore.