I was also curious. Go and microcontrollers? Must be a misunderstanding and not Go the language.
Memory-mapped I/O is possible, but there's no way to separate such unsafe constructs from "safe" ones, as that essay points out.
Additionally, they maintain an IDE, a complex set of pre-processing tools, and library+device management servers that allow more modularity in the ecosystem.
I'm sure there's a place for Go, I'm just not sure where they plan to put it.
Source: I write Go code that runs on microcontrollers.