Microsoft last month asked HTC to install Windows Phone as a “separate option” on Android handsets, and offered to “cut or eliminate” the license fee as an incentive.
This strategy is unlikely to work, Dual boot devices were never popular in the PC era, leave alone the era of mobile computing where simplicity counts. Smartphones are not so much popular because they ask for know how of geek-y stuff to Dual boot.
Instead, i would say Microsoft should leave the OS platform level to Google and compete on the services level. Microsoft has competing products to the services offered by Google, for Instance, Bing competes with Google Search, Hotmail/Outlook With Gmail, Skype with Hangouts, Bing Maps with Google Maps, Office 365 with Google Docs, Skydrive with Google Drive, Internet Explorer with Chrome. Microsoft could emulate the success of Google Play Services on android with its own competing service with its core services bundled replacing the core Google services. It will help eliminate the problem of app unavailability on Windows Phone and Microsoft will be better able to compete with Google for ad dollars.
Now it remains to be seen, If Microsoft will be able to make an OEM produce an android device with Microsoft Services replacing Google Services. That would be a really nice mobile transition for Microsoft going forward.