There's a new philosophy in World of Warcraft Power leveling, when it comes to who you should bring on your raids. In short, as the headline says: pick the players you like, not the classes and specs you need. In all of WoW power leveling until this point, there have been certain specs that were virtually required in various parts of the various raids. Which specs these were has changed with time, but think of Shadow Priests' mana battery capabilities, or stacking Shamans to get many Heroisms/Bloodlusts. To be a cutting-edge raid it was simply required to prioritize "correct" raid composition over other factors. Yes, your players needed to know how to play their class, but beyond that, you took what was needed for the fights you were doing. And you took a Warrior main tank, generally speaking.
All that is set to change forever in just nine days. Now the classes are much more interchangeable with each other than before in the process of World of Warcraft powerleveling . Some prominent buffs have been nerfed, and in one notable case, distributed: Shadow Priests, Survival Hunters, and Retribution Paladins all give mana back with Replenishment. In general there is more than one class that can provide most types of buffs and debuff. Also, many buffs that used to be group-wide are now raid-wide, such as Paladin auras and Shaman totems. This makes it much more likely that picking two tanks, three healers, and five DPSers out of a grab bag will get you decent coverage on buffs and debuffs.
Personally, I find this a very exciting trend. That might just be because I mostly play hybrid classes, but honestly, six out of ten classes are not pure DPS classes when we do WOW powerleveling, which at least to some extent qualifies them as hybrids. After all, this game is about fun, and I never have more fun than when I'm playing with friends. We shouldn't have to choose between fun and success.