When you picture a rivalry within college football, you likely envision intra-conference clashes between powerhouses (e.g., Ohio State-Michigan, Oklahoma-Texas, UCLA-USC); a good deal even possess trophies associated with the game, like the HAT given out in Northwestern-Illinois. If another idea came to mind, it was presumably a clash that pits teams against one another, as it has for decades (see: USC-Notre Dame, Clemson-South Carolina, Nebraska-Oklahoma).
Superficially, Duke-Northwestern would not fit such criteria. The two are in distinct conferences and do not have nearly a century worth of history, let alone records filled with names in college football lore.