In short, instead of 1 Block per year made up of 3 sets and a stand alone summer Core set, we will now get 2 Blocks per year comprised of 1 large set and 1 small set. Core sets are gone now.
Also, Standard format, starting in 2016, will be composed of 3 Blocks and we will experience rotations in both the Spring and the Fall.
I’m dubious of this change, but we’ll see how it works out.
Especially key is that Khans of Tarkir will only be in Standard for 18 months, instead of 2 years.
As always, hunt bigger game!