The open sourcing of Roslyn can only mean good things for Xamarin.
I think you wanted to say that the "change" was made only thanks to the exit of Ballmer, but I think that's an exaggeration.
I think it'd probably be more accurate to say that these particular changes are symptoms of the same corporate change of direction that the change of CEO was, not that the change of CEO specifically resulted in these releases.
How about in 5 months? Don't get me wrong I'm not falling on either side of this argument, but I think it seems at least slightly plausible that this process could have been initiated or at least accelerated by the new CEO.