I don't think you have much to worry about. The airline industry has been focused on fuel efficiency for a long time now, and as a result, coast-to-coast flights already take significantly more time because they fly slower (for fuel efficiency). Unlike the 60s, air travel is no longer the domain of the upper-middle class and up, almost everyone does it, and the airlines profit through sheer volume, and live with a lot of competition. This is why they're always trying to weasel more profit with little fees for everything, because consumers are so price-conscious. They're not going to get that many takers if they start offering flights that are 2-3x the speed but 6x the ticket price.