Globally over the entire console's life time?
It's definately possible if Microsoft doesn't take the right steps, but will it happen? I don't think so.
I think Phill Spencer is going to stear Xbox back into a more prominant position where they can at least compete with Playstation 4.
I could see the end generation sales being something like:
Wii U: 25M
Xbox One: 80M
Playstation 4: 120M