Politics and language wars aside, it could look exactly the same as the current Windows Phone. The language used to implement an OS has no bearing on the visual appearance, UX, etc. I wouldn't expect the performance to be much different either.

BTW, you can write apps in Go on Windows and run them on Windows. Don't know how different the tooling would be for Windows Phone.

And then? Who cares about what language the OS is written in? Customers surely don't.

Investors would be outraged by the stupidity because Windows Phone runs Windows.

Most investors don't care about the technology. Does it make more money or not? And I would doubt that changing the programming language would make any difference to the market perception of the Windows Phone as a product.

Techies who favour Go might as well just buy an Android phone.

As you observe. rewriting Windows Phone in Go would not implicitly make money. My observation is that rewriting a vast field deployed code base [even one smaller and less widely dispersed than Windows] in the language of the month is frequently a bad idea because it introduces regressive bugs.

Beholden to Wall Street since the recent divestments of Gates and Ballmer, a shift such as that suggested would trigger action by investors as shareholders in response to the utter management incompetence it suggests.

You already answered the question - "They will be thinking wildly" :)

While GO is a great language, I doubt it has any significant advantages over C#. Also, Microsoft is doing very well with the phone dev, its the end developer who're not writing apps. And they are not-not writing apps because of PL issues, C# is much more popular than Go, they are not not writing because they are trendy.

you do realize the OS itself is probably not built with C# right?