After trying to outcompete Apple with similarly closed but way crappier controlled and closed environments (Windows 8 store and metro UI), they finally understood they had to push their own strength, that is: "developers developers developers developers".

This might just be another embrace phase. They have been cyclical in the past. If they were to get a large portion of market share on their proprietary tech platforms they would certainly move to lock in their users and cripple the open platforms they are now adopting. They are only restarting the cycle because they are losing ground.

And I'm not coming at this from a malicious Microsoft angle, they are just in the same league as Adobe and Oracle in that they maximize revenue by dominating markets and crushing competition to force users onto their proprietary platforms. It is inherent to how their principle earning divisions operate.

This makes no sense to me. There is no opportunity for "extend" or "extinguish" for either StackOverflow or GitHub. Similarly, if they ended up destroying the various non-microsoft .NET implementations (mono..), it would affect the platforms they run on very minimally. There'd be a couple of pissed off people, but meh.

Exactly, I don't see them open sourcing Office or Windows any time soon.