No, flipping, thanks.
Surely microsoft can, you know, pay you for the copyright if they want own it when they decide to merge your work? Or just take it on the same license. And as far as providing legal guarantees for microsoft? Yeah that's gonna be a no from any sane individual. Perhaps a big company like google might agree to those terms but also, perhaps not.
So no they don't want you to contribute, at all, or they'd do it right.
This looks quite disappointing. But as noted elsewhere you can read some source, or fork and refuse to contribute back I guess... But why?