What good will physical switches do if a virus is waiting for you to flip that switch to write-enable so that it can now infect the HDD firmware? Switches would be useful if you never update the firmware. In which case, eliminate the switch and make the firmware permanently read-only. My point is, we need a more secure way to update firmware.
Unless the virus is resident in Bios, (which can also be protected in the same manner), it would be impossible to be infected if you are in a power off state, then enable your switch/jumper, power on, flash your firmware, then disable the switch/jumper after completion before booting into your OS.
In the old floppy days things were pretty much this way. Time to go back.