Google isn't in the business of making phones. Google is in the advertising business. Android is simply a delivery and collection system for their product - aggregated customer data for targeted advertising. They don't make money from developing Android and giving it away.
I think as Windows 8 and Windows 8 RT proliferates it will be hard for any develop to ignore the platform. Really, it is a genius idea by Microsoft as there is no way, competing head-to-head in just the mobile space, they could have caught up to iOS and Android when it comes to app availability. With Windows 8 they can essentially combine the customer base from three different devices into one.
While I am sure Google would relish the idea of controlling the bulk of the mobile market - and all the customer demographics and info that come with it - it is probably a far fetched idea. Apple doesn't like to share control of anything and would sever them completely from iOS if they could. The worst thing for Google isn't that people give up on Android...but they start finding alternatives to GAPPS. That will happen if Google doesn't make a serious bid to get on as many platforms as possible. So while Google may not want to get saddle up with Microsoft it is probably in their best interest to embrace the Windows 8 ecosystem. It is unrealistic to think that the Windows ecosystem is going to collapse all that soon no matter how much pressure you put on it with your $250 laptop or free phone o/s.