First IronPython & IronRuby (http://news.ycombinator.com/item?id=1833772 ) and now this. I have to say, Microsoft is (or seems to be, depending on your philosophical disposition) increasingly embracing FOSS, and that's a very good move not only for them, but also the community.
You're not implying that nobody uses F# or IronPython, right? That aside, I'm not in a position to know their motivation behind it, I can only say it's a good move for the FOSS community.