Here's my logic:
- Microsoft want to get people building Android apps to build Windows apps. Getting them on the OS and using the tooling is a good start.
- If building in Visual Studio, on Windows, it would be a smaller step for Microsoft to make to get them to build for Windows.
- If VS was extended to build Android apps in Java, They'd be one step closer to enabling building Windows apps in Java.
- Visual Studio is a shell that can be "easily" extended to support different languages, etc.
- VS 2015 already includes an Android emulator. - Did they really just add it for HTML5 based apps? - We know how popular those are ;)
- VS tools are widely considered as being the best IDE in the industry. Tooling for building Android as is widely considered as being some of the worst. I think it would be an appealing proposition for developers building Android apps.
What about Xamarin (and their partnership with Microsoft?
I don't see an issue. They're both targeting different audiences. Xamarin are appealing to those who already have .Net skills and helping them build for Android and iOS. This would be about getting people coding in Java to build for Windows.
And of course, I wouldn't speculate on anything like this if I knew even a tiny fraction of it to be true or related to any NDA I may or may not have signed.
If any of the above turns out to be fact then it's because of my knowledge, insight and, most importantly, luck!