GPLv3 = release code, cannot link to proprietary software. For some graphics chipsets some company might (need) to do that. Then you'll need to go to Canonical to get Mir under a special license just for your company. Then Canonical gets some money.

I have nothing against Canonical wanting to follow this. I do not like only one company being able to offer a different license (their CLA). So anything like that is a no-go for me.