I don't think Microsoft could support an Xboy properly, they couldn't support Xbox 360 properly since Kinect came out. So it would flop. I get the impression, WP8 is microsoft's portable anyway.
Xbox One, PS4 and Switch (+ Many Retro Consoles)
'When the people are being beaten with a stick, they are not much happier if it is called the people's stick'- Mikhail Bakunin
Prediction: Switch will sell better than Wii U Lifetime Sales by Jan 1st 2018