Simple and straightforward question. I think 30-35 million lifetime would be the starting line for a successful console. Anything more is icing on the cake, and anything less is another nail in the coffin.
"Games are a trigger for adults to again become primitive, primal, as a way of thinking and remembering. An adult is a child who has more ethics and morals, that's all. When I am a child, creating, I am not creating a game. I am in the game. The game is not for children, it is for me. It is for an adult who still has a character of a child."
Shigeru Miyamoto