I see. I'll read the article this evening if I find some time. 
The way we implemented it for the next version is that if you (and your opponent) don't offer first class on the route, they try to fly business class. (or any lower class if they must)
This is also true if any class is full, they look for a lower class.
There are 2 things we have to add though:
-if you (and your opponent) make a class too expensive, the passengers will just not fly at all, rather than looking for a lower class.
-if you make the higher class not that much more expensive than the current class, passengers won't change their mind and still won't book the higher class.
I think with those features implemented we come close to your suggestion?
The way we implemented it for the next version is that if you (and your opponent) don't offer first class on the route, they try to fly business class. (or any lower class if they must)
This is also true if any class is full, they look for a lower class.
There are 2 things we have to add though:
-if you (and your opponent) make a class too expensive, the passengers will just not fly at all, rather than looking for a lower class.
-if you make the higher class not that much more expensive than the current class, passengers won't change their mind and still won't book the higher class.
I think with those features implemented we come close to your suggestion?