During my university days, Dad used to buy me a MAS 12-month open-ticket to Perth. I would then have the option to nominate my return flight date as and when I wish to fly home. The cost of this ticket is of course much more expensive, but I needed that flexibility depending on when my exams ended.
Then came AirAsia where they are significantly cheaper if you book up to 12 months in advance, and a change of date will impose a penalty, and you also have to pay for the fare difference. Most of the time, it would be cheaper getting a new ticket than trying to change the date of the ticket.
AirAsiaX has now come up with a solution in what they call a Flight Pass. This is purchased via http://www.optiontown.com