Also, the equivalent would be “Heads should roll. Just right onto the carpet of the Oval Office, as a warning to federal bureaucrats.” When you elaborate graphically, it becomes much more of an actual call for violence. At the very least it’s in poorer taste than the idiom usually is...

Not supporting Bannon at all here but I knew what “head on a pike” meant immediately: “to be made an example by those in power”. So did my 13 year old, so it’s not generational. He also mentioned something about a Harry Potter reference.

It’s not an uncommon phrase at the very least. I know I’ve heard people use it in business settings, just like folks sometimes use phrase “heads will roll” in otherwise polite conversation.