The end result with the testing is a Windows 10 flavored Xiaomi Mi 4 that features all of Microsoft's mobile services. Consider this a simple customization of an Android device with the Xiaomi Mi 4 user opting to install a ROM containing Windows 10 instead of Cyanogen, for example. This ROM allows the Android user to have close to a native Windows 10 experience on his phone, which Microsoft hopes will be so positive that the Android user switches to Windows 10.
Xiaomi's handset is just the first being tested. Eventually, Microsoft hopes to have similar ROMs available for other Android phones down the road. The company picked Xiaomi first because its customers provide feedback religiously on Xiaomi's weekly software updates.