Here’s a hot take for you. I think putting ketchup on a hotdog makes about as much sense as putting maple syrup or peanut butter on it. The flavour and texture characteristics of the bread and the sausage, in my view, are such that you need a bold, sour flavour to complement them, ideally with some crunch. Thus, I think sauerkraut, or raw onion, or mustard, or pickles are ideal toppings for a hotdog.