Unity is free to use Mono commercially under the existing open source license, so long as they contribute their changes to the Mono runtime. They can even take

Unity is free to use Mono commercially under the existing open source license, so long as they contribute their changes to the Mono runtime. They can even take advantage of this without making any of their own code open source, because Mono is licensed under the LGPL, not the GPL itself. Xamarin has made it very friendly to use Mono in commercial products without getting paid for it. I don't see what's distasteful in asking people to pay if they want license terms that go above and beyond what the LGPL offers. The commercial party gets the additional licensing features they want, and the money funds further development effort which goes to other users of Mono, both paid and libris/gratis users under the LGPL. Everybody wins.