Just for your last two sentences. No. MS hasn't changed much. They noticed that after losing in mobile, they also started to lose developers as well. So they are just trying to look cute.
I will perhaps re-iterate my thoughts once Ms stop extorting Android device manufacturers for BS software patents. Until then, I am not touching anything from them.
I can't believe I'm defending Microsoft, as I was a hardcore Linux guy back in the days.
To answer your question, Microsoft is not only about mobile. Their work on Roslyn compiler, F#, Reactive Extensions, SignalR, ASP.Net vNext etc is high quality open source. Moreover if they make their tools open and play nice with Android/iOS etc, we all win, right?
I will perhaps re-iterate my thoughts once Ms stop extorting Android device manufacturers for BS software patents. Until then, I am not touching anything from them.