Go uses the Plan9 assembly syntax but doesn't support GNU asm syntax. gccgo uses GNU asm syntax but doesn't support Plan9 assembly.

The Go linker doesn't allow you to not link in the Go standard library runtime, which means you need to use gccgo to write a kernel.

The end result is that you can't do something that's buildable with the standard Go toolchain, and even if Go were to add a "don't link the runtime" option there'd be no way to incrementally port your ASM over one bit at a time. It's all or nothing.