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.