Coffee really complements certain fats on my palate. Avocado and coffee taste like magic to me. Some cheeses too. Peanuts and almonds are good too. Bacon and eggs are fine, but not particularly special. I love coffee and a simple 80/20 hamburger with mayo and potato bun.
Poking around online, I do see some non-traditional red-eye gravy recipes that also add milk.
Bacon and chocolate is also a well-established pairing.
Honestly, assuming you can deal with the oiliness, I think bacon flavor would work great in a coffee drink.