If I were in the position at Microsoft to institute a pirate dual-boot development campaign for Windows Phone, I would have a lot of fun doing it. Generate market buzz for Windows Phone by giving those with suitable devices the opportunity to install a "free operating system upgrade".
The challenges would be as much legal and political as technical - working with OEM and carrier partners who're nervous about unlocked bootloaders, etc. A marketing campaign that isn't about getting people to buy new hardware so much as giving new life to devices already out there... I would target recent Google Nexus devices (they're open, right?), then do an assessment of iPhone 5* and the legality of a push-button JailBreak app: "Tired of your stuffy iPhone? click here for some open Windows". yeah, redmond could have fun with this and make some noise where they need good marketing more than anything, Simply put, I would look closer at Windows Phone for my next upgrade if they did something like this. Do something nice for the enthusiasts and influencers, etc.