For those that do not follow the spoilers, Onslaught Fetches are getting reprinted in Khans of Tarkir.
What if i still don't follow?
Fetchlands are a cycle of 10 lands which search your library for another land with one of two basic types (for the cost of 1 life). Example:
Misty Rainforest . Do not that they are able to search for dual lands with basic types, such as Volcanic Island and Overgrown Tomb.
First cycle of 5 lands (only allied colors) was printed back in 2002 in Onslaught. They are Legacy staples, played in basically any deck that plays lands. They were not available in Modern.
Second cycle of 5 (enemy colors this time) was printed in 2009 in Zendikar. They are both Legacy and Modern staples, seeing play in all decks. With the rise of popularity of modern and new influx of players, their price skyrocketed recently.
Now, when they print the old fetches now, they WILL be available in modern, and are a kind of a entry card for legacy, so everybody is looking forward to them!