It doesn't seem like a lot of work. We've already paid for them. I've heard (from an insider) a rival franchise who shall remain nameless, is hoping to be the first to do this. Won't their fans love them.
In every new game, there are specific new maps and new features of the game. It depends on the theme or on how the development team prepare for it or layout it. And every game is different to other games but that is a great idea though