On one hand, I think the history is enough to be highly skeptical of MS: how many times does someone have to show you who they are before you believe it?

But that aside, I don't see how any corporation should be trusted to host such a large percentage of OSS. Whether it's a year from now or 10 years from now, what do you expect to happen when Microsoft's material interests cease to align with supporting OSS? Do you think they will subvert their own interests in the support of some "greater good"? Given the history of how corporations behave, I think that would be very unlikely.