Windows 7 source code shall enter the Commons regardless of Microsoft's wishes
Sooner or later, the entire Windows 7 source code will be published on multiple dark recesses of the Internet and parallel peer to peer nets. That is inevitable because digital sequences (in this instance source code files) cannot be corralled indefinitely. No matter how hard people try to contain sequences published for commercial purposes they succeed only for a short interval, this determined by how keen people are to get their hands on it. Proprietary source code takes longer to leak out than compiled versions but is certain to happen in Microsoft's case.
The sheer size and complexity of Microsoft's development apparatus makes maintaining absolute code security difficult. Moreover, resources available for security are best targeted at software still in production. My understanding is that Windows code is released to a privileged cadre of trusted external developers because it is in Microsoft's interest so to do. There must be numerous copies of Windows 7 code knocking about outside Microsoft, some perhaps 'borrowed' by Microsoft employees. These will range from the earliest Windows 7 versions through to final release.
Unofficial release of Windows 7 code will leave Microsoft with egg on its face: far better to garner credit by showing generosity. Perhaps it will spawn an underground hobbyist movement. It will pose no commercial challenge to Microsoft. Even should recompiled versions with enhancements circulate there will be no observable impact on Microsoft's revenue from routine price-gouging.
Linux Wine developers can do something useful with leaked code. Because of egregious copyright/patent law they will be obliged to include paraphrased Microsoft code in Wine source releases. It seems only fair given that Microsoft is drawing freely upon open source Linux code.