I had a similar idea, but just as a trial - on one of the game worlds allow players to act as manufacturers (although no deviations on a/c designs). Should be a simple tool, invest money to expand factory - increase rate of production, adjust pricing, reduce capacity significiant if there is too small demand, be more flexible on discounts... Maybe then the marked would look a bit more realistic. If you are Boeing, you would try to kill production line of B737Classics as soon NG`s are out (or F27/50 and F28/100 example). The same applies about pricing - example of B73C and NG`s. In GW2 now (2005) the price range for classics are 28-39m, for NG`s - 65-98m. If that was controlled by player, for sure he wouldn`t keep classics line alive.
Maybe if we would be able to try to make a business from other side as well, the game would be more tricky and challenging. The same could be said for leasing companies.