This might not be news to a lot of you but in the time I have spent traveling we referred to this kind of ticket as an open-ended ticket and they were always substantially more expensive than a standard ticket where your dates were defined well ahead of time.
Because of the downturn in the airline industry almost all airlines, including a few of the budget ones, are offering relatively unlimited ticket changes over the course of A FULL YEAR without any penalty or surcharge for the changes regardless of how many times you do it.
I'll use my friend who is Canadian and currently has a one way ticket to Mexico City planned for "sometime" in the future.
He is getting tired of the Canadian winter and well, things are only going to get worse for him as the months go by. For now, the weather where he lives is still bearable but after years of living there he is very aware of the fact that it shant be long before the temperature drops to "kill you" levels in 30 days or so.
There was a special offered by Air Canada for these sorts of tickets and he jumped at the opportunity.
When he booked the ticket they didn't really seem to care what date you had your outgoing ticket for because they are extremely aware of the fact that people are buying these tickets simply to put it in the bank and use it at a later date. Since then he has changed his flight twice and neither one of those times was he charged anything other than the price difference between the two tickets for the pleasure. In one of the instances he actually got a couple of dollars refund because the new date was cheaper than his original fake departure date.
Now maybe this doesn't seem like a big deal to anyone out there that is not an avid traveler but for a backpacker or flashpacker like me, this is a huge development and a wonderful reason to choose one airline over another.
In the past I have had certain travel dates that I was relatively certain that I was going to stick to only to end up somewhere with a great group of new friends and I wanted to extend my stay. My desires were squashed when I was told by my airline that changing my flight was going to cost me several hundred dollars just to change to another date and I also had to pay the difference between the two fares as well. This is obviously a money grab on the part of the airlines and because everyone was traveling back then, they didn't even have to remotely try to accommodate you or even be nice.
These days, since the supply exceeds the demand by at least a ration of 3-to-1, airlines are doing whatever it takes in order to get your business. Many airlines, including Air Canada have experienced massive layoffs.
There is one thing that you need to be certain of though. Make sure that the change of date is something that can be done online because most airlines and in particular North American ones have rather extreme call center staffing shortages at the moment and if you need to speak to an actual human in order to change your flight you are going to be in for a bad time. The last couple of times I have had to deal with a North American airline the wait times were so atrocious that it was actually less time consuming for me to drive 45 minutes to the airport and get it taken care of at their offices there. Most of these local offices won't even answer the phone and simply redirect you to the national or international call center - and this means you are going to spend hours on hold. Air Canada's system is so backlogged that they offer to call you back and this is only marginally better because that callback might happen in the middle of the damn night and if your phone is on silent, you will miss the call and they only try to reach you ONE TIME.
So that's just a little bit of a warning about how this "deal" could go wrong but if you poke around the various websites you can get a really good deal that as far as I am aware was not something that existed without a fee in the past 20 years.
Also, make sure that you book directly with the airline and not with a 3rd party website like Expedia. If you book through a 3rd party website the policy of free changes to your ticket most likely will not apply as they will tack on a fee and screw you over this way. 3rd party websites, in my experience in the past year, are not cheaper than booking direct anyway, so there really isn't much reason to use them.
So even if you are not sure when you would like to travel it might not be a bad idea to go ahead and book one since as soon as the world goes back to "normal" (if it ever does) these courtesies will almost certainly be some of the first to be eliminated.