This "attack vector" is relying on the fact that you get physical access to the targets router/switch, so you can connect to the network and I think network admins would stop extra PSU in their networking closet pretty fast.

Which started me thinking... What if you would build RPi or similar small device into a router's casing and made it act like a router on the same time. Obviously you'd have to have some way of copying configs over from the old box to the impostor box, but it could be harder to spot since there wouldn't be any extra hardware.