Light load routes would ultimately get canned.
A trip to the USA with QF via Auckland, was full to NZ and around 25 people on-board to LA - prob a decade ago now but that route is no more......
PS Going to Perth ON 18 Jan 6.25am, there were maybe 20 PAX. The seat map showed the story so one could upon getting a handle on it, work out how many seats were generally filled on the seat map and then on the actual flight.
BITRE releases monthly stats as do airlines advice actual loading in their quarterly and annual reports so you could work out a kind of average, seasonal loading. Momondo was showing seasonal pricing so this could be useful too as lower pricing for longer (as well as points seats availability) coming Upto the day of travel suggests more vacant seats