Airlines have, in fact, toyed with the idea of an all-you-can-fly ticket based on a fixed fare.

For example, American Airlines launched its AAirpass in the early 1980s.

It promised unlimited lifelong first-class travel across its network in exchange for a one-off $250,000 payment, a price tag that was revised upwards to $3 million in 2004.

The scheme seemed like an easy way to get up-front cash at the time but ended up being a drag on American Airlines’ finances, since the handful of people who signed up turned out to make, understandably, extremely intensive use of their acquired privileges.