The significance of this achievement is that microcode and its update mechanism has been historically undocumented and hidden from public scrutiny by processor

The significance of this achievement is that microcode and its update mechanism has been historically undocumented and hidden from public scrutiny by processor vendors (AMD and Intel in this case), while at the same time the lowest level of abstraction in a computing platform and thus extremely powerful. However it is not unreasonable to consider that well funded state actors have developed microcode exploit technology that would make their control over a system undetectable and impossible to remove. The recent leaks have shown exploits that target hard drive firmware for example.