This is surely a policy shift for Microsoft, in it's own small way. I cannot see it as a revolutionary step, which is how some are depicting it. The company known for it's arrogance is bending a little bit. That's all. The world has not ended and you don't need to pack your snow shoes when you die.
That Microsoft is inviting in open source projects where previously only ISVs producing proprietary software got in is merely an acknowlegement of the fact that many open source projects have resulted in major products that have to be accomodated. Period. There is no more to say about it.
I expect we will hear similar news for some other projects, such as MySQL, Apache and perhaps some of the other open source databases.