That is exactly the strategy i use when i am not sure where and when to go. Then ticket some intercontinental flights.
It is also possible to book/pay only 3 continents and then add continents for the difference in the original fare.
This works great for my ex CAI travel. Just book CAI-Europe and three continents and some other flights. It is even possible to change the direction of travel (West to East) when in Europe.
Yes, you need to pay the change fee, but this way you stay extremely flexible.