As I understand it, you would need to have an existing RCE to exploit the microcode patching process.

h0t_max’s research means that future attacks — once your local machine has been infiltrated by some other means — can do a lot more damage than simply encrypting your filesystem or sending spam. They can rewrite the way your CPU works.

When your OS gets attacked by malware it is attacking the layer above the bare metal on which your OS runs. The base hardware remains untouched. You can at least clean things up by installing a new OS on the bare metal.

If malware attacks the bare metal itself, then you are stuck out of luck.