adityapratama: if people would leave because they get bored of lack of competition, then there would be NO mega airlines so mega airlines and people leaving can not both exist, mega airlines would have higher rates because of possible (but again not garunteed lack of competition) so smaller airlines could come in and get a foothold providing lower rates, even if the mega airlines cut there rates to less profitable, the small airlines could open up at airports that everyone says will be ignored, giving them an option to grow, and they could grow enough to be able to compete with the mega airlines.
Problem with that scenario is that the majority of those players who start anew in the middle of worlds don't have the know how or the ability to find those small unused airports. As of right now, there are plans to try and update the wiki, but that will take time. In the mean time, we'll have the majority of people who don't quite understand the intricacies of the game whining and complaining in chat. If anything, these worlds should be marked expert (like S2) and should have stricter rules concerning the successful operation of such airlines. That should discourage the newbies from entering the world (especially if it is an open world, which is a popular place to learn how to play). I'm still not sold on the 50 year duration, because even the mega airlines will get bored and go stagnant after 20-30 years.