While I'm not entirely sure what the strategy is with this, I'm fairly surprised by the move. This is something that would have been unheard of from Microsoft even a decade ago. They've made a bunch of really huge strides in FLOSS, but they've all been centered around developer mindshare. I totally get open-sourcing your developer tooling, especially in consideration of their Azure ambitions, which isn't bad.
I really like VS Code, which has become my daily editor of choice, I keep meaning to try the integrated debugging, but haven't. The .Net core releases have me looking at C# again, in a fairly new light. The Linux Subsystem for Windows is impressive.
All of that said, this move still surprises me. I'm not sure if/how much it will benefit the larger developer community, but it is really nice to see a much more open MS. All I can say is that the next half decade will be particularly interesting in terms of software improvements as hardware has started to level off.