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.