I doubt there is any straight answer to give on that, but one issue is going to be leasing and purchase costs. With loan money and interbank trading being depressed, several airlines have allegedly found it hard to finance deals with the likes of Boeing and Airbus that were placed in the happy times. The finance rags have even hinted at credit deals being unilaterally cancelled with a couple of companies as the banks no longer wish to do the deals.
Lessors such as ILFC also do not have a vast pot of cash available in the same way. So in the next few years we could see capital costs rising due to more expensive credit as banks and lessors price their wares higher to the airlines.