You may not impose any further restrictions on the rights granted by the GPL.But going up against Microsoft lawyers on this matter would be much harder than going up against SCO lawyers.
It's classic Microsoft (what's the phrase commonly used?) embracing and suffocating of competition.
I might add: Ripping off someone else's work, selling it as your own, or giving it away to drive them out of business.
Embrace, Extend, and Extinguish™.