Well, it's absolutely worth remembering that Arduino the ecosystem is much larger than 8-bit uCs. Arduino now supports from tiny 8-bit uCs with hundreds of bytes of ram to expansive ARM devices comparable to those you'd find in drones and other large devices.

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.