I don't see this rotation drastically altering the format like past rotations have. Most of the top decks still exist and are actually viable, and the only Tier 1 deck that we really lose is CMT. I guess we also lose Speed Darkrai with Smeargle leaving, but the main compononent of that deck, Darkrai, is still present. Zekrom/Eelektrik and Darkrai are still here, and it seems the new set will be changing decks more than the rotation itself will be. We gain Darkrai/Hydreigon and Garchomp/Altaria, as well as possibly Eelektrik/Rayquazya, or at least Rayquayza in Eelektrik variants as a tech.
Past rotations have revolutionized which decks can be played and are viable. For example, this past one that went from MD-On to HGSS-On made all the top decks obsolete. LuxChomp, DialgaChomp, SableLock and other SP Variants, Gyarados, and Vilegar were all completely gone. The format was left to be explored and figured out, and it was still being explored up until Worlds/Nats, when people jumped on the Yanmega train all of a sudden. This next format is pretty predictable already, and there isn't very much exploring to be done. The top decks should be Darkrai variants, Garchomp/Altaria, and Zekrom/Eelektrik. I'm sure there are some tier 2 decks I'm missing, though.
Still, my main point is that this rotation doesn't bring new decks to the table, nor does it make very many obsolete. It will change how decks are built a little without Junk Arm, I guess. It will also force people to play more conservatively with their trainers, especially Catcher and Switch. Still though, this rotation won't be as groundbreaking as past ones because of the insane power creep starting in BW, which has made the majority of HGSS cards, mainly attackers, completely useless and unable to stand up to the high HP and damage the BW cards have to offer.
Anyway, my point is that this rotation doesn't really affect players very much, especially in comparison to past rotations.