The annual Standard Rotation has been announced: the new Standard Format will be the sets XY-BREAKthrough and on, effective September 1, 2017.
Some cards of note that will be leaving the Standard Format include Shaymin-EX, VS Seeker, Trainers Mail, Lysandre, Forest of Giant Plants, Team Magmas/Aquas Secret Base, Sky Field, Mega Rayquaza-EX, and more.
A Standard Format without Shaymin-EX, Trainers Mail, and VS Seeker seems like it will run a little slower. Thankfully we have Tapu Lele-GX to search for unused Supporters in-deck, but after rotation most decks will probably not want to run one-of supporters, instead including 2-4.
While the format will be losing the popular Lysandre, the upcoming Burning Shadows set includes the similar Guzma supporter. Guzma acts like a Lysandre, bringing an opponents Benched Pokemon to the Active (your choice), but it also switches your Active with a Benched Pokemon (like an Escape Rope but the user chooses both Pokemon).
Its also worth noting that Forest of Giant Plants will be banned in the Expanded Format when rotation occurs, along with the Archeops that prevents evolution. I guess that means no more turn 1 Vileplume item lock in any format.
Burning Shadows Coming Soon
More Sets Later
After Standard Rotation, we have more sets to look forward to! In addition to an upcoming quarterly expansion set in November Crimson Invasion well also be getting a special set (similar to last years Generations), called Shining Legends, available in October!