Marlin spikes are common on sailors knives because they traditionally did a lot of rope-splicing and knotwork. These days that sort of thing is pretty uncommon, so you're unlikely to see a marlin spike unless that person is also a knot hobbyist.
While I do appreciate the charm of the old-fashioned sailors knife, I don't have one yet, and I don't consider a marlin spike to be a daily necessity yet.