It would be a major overhaul of the way of thinking lines, though. Real life example : WIZZAIR flys a A320 between Beauvais-Tillé and Wrocław twice a week. That's a low-cost flight. It's nearly full during holidays, and rather full off-season, so probably 250/300 pax per week. In 2014. That's 40 pax/day, roughly
In game terms, even a CRJ100 would be overdimensioned. Most people flying this plane are bound to take it anyways, as the only alternative is 17 hours of bus. In GW3, it currently has 14 passengers per day - 1999. But even with such a low demand, a CRJ100 twice a week could fdo the trick.
I completely agree with the idea of separating classes, though. First class flyers would never wait. Business really not much. Economic have no choice, and will push back their flight for a few days.
Could be an accumulation. Let's stay on this line. Demand is, from monday to sunday :
15-13-13-14-15-12-12 - that's unflyable.
Monday ; 15, no flight
Tuesday ; (15*0.75)12 + 13 = 25, no flight
Wednesday ; (25*0.75)18 + 13 = 31, flight
Thursday ; 14
Friday ; (14*0.75)10 + 15 = 25
Saturday ; (25*0.75)18 + 12 = 30
Sunday ; (30*0.75)23 + 12 = 35, flight
That's flights with 31 & 35 of potential, Meat for a small Embraer, and the line is now playable. And somewhat realist. you go down from 94 to 66 potential pax, but at least you make some money.
count 25% instead of 75% for Business, 10% for First class, and you've got something interesting.
For simplicity's sake, it would go back until the previous day with ANY flight, not counting excessive passengers. For example, even if my plane is a 30-seater, it would still begin at zero on mondays and thursdays, on my example.