[ybx]

Forking isn't possible when the code is not there, and when the company that created/copyrighted the code is openly hostile to forks. By them releasing under MIT, this issue is resolved.

As for the manpower behind Microsoft, git has made it very easy to merge code from relatively similar source code - in the cases that they make large important changes, those can always be merged in, and usually without too much work involved.

The only way they could succeed with something like that would be for them to go closed-source again, in which case you're still better off than if they never went open in the first place because you still at least have some code to work from.