Actually, to be on the dot only when an update adds something major that needs to be generated in a new area of the wild
The only reason it NEEDED to be updated before was the change from the old map system to Anvil, and this was not completely required, but gave us the ability to add to the world height, and all new generated things require Anvil. Unless some major change comes like that again, a full wilderness reset is very unforeseeable. As long as Minecraft sticks to Anvil, they have given quite the ability for any new generated structures/biomes/items to spawn as long as they are in new areas, unless it gets to a point where players have to travel 100k+ into the wild just to see a new feature, nothing along those line will really warrant a reset. Even then, future updates planned for EMC itself will make deep wilderness travel even easier.
go to http://htwins.net/scale2/ then zoom out to 17 to the 8th power (when you can see neptune and uranus) the minecraft world is 64,000 KM