Microsoft doesn't need a credible competitor to Android at all. Anything they do in mobile is pure gravy. They're generating $20 billion a year in profit without one, and have seen zero meaningful harm to their profitability over the last five or six year rise of Android. It can easily be argued Microsoft will make a lot more money building software for Android and iOS, rather than competing with them. Office is more valuable than either Windows or Android. Azure is going to be a more valuable business than Android is for Google.