It was stated in the General forum that the demand system is about to be overhauled.
I have a suggestion in mind while you do that that would (IMO) bring more realism to the game.
In real life, when people book their trips they most of the time want to come back too. In AS however all trips are booked one way. Not many people would do that in real life, for example fly Albany-Chicago-Las Vegas on American Airlines and then book the return trip Las Vegas - Minneapolis - Albany on Delta. No, they would do the round trip either with AA or DL for a multitude of reasons (Frequent Flyer programs, Image, Pricing etc).
So in the new demand system, please consider to change that so that the pax would only book A to B via C on airline X (and its IL partners) if the same airline (together with it's IL partners) can also provide the return trip B to A via C or D at least some days of the week.
Or alternatively at least inflict a severe ORS penalty if that is not the case.
Why would that matter ? It would force the airlines to make their wave systems work both ways from the beginning. That means that you cannot "cherry pick" routes in the beginning and it would slow down growth. Later in the game most airlines would satisfy that requirement anyway so it does not hurt anyone in the long term.
Another suggestion. At the moment the PAX do not care what time the flight departs. In reality most pax would really try to avoid red eye departures if they can. In reality especially commuter planes do not run nonstop all through the night. They stay at the outstation overnight and leave early in the morning to catch up with their hubs first connection wave. So my suggestion is, that for flights less than say 1000 km in length, inflict an ORS penalty of some sort on all departures between 0000-0500 local time.