With the Season of Mastery, the intent is to make everything a faster paced fresh start. Because of the intention to release everything quarterly for a year, there are a series of content adjustments to expect.
The Dungeon Set 2 questlines will be available at launch and many other dungeon and reputation items will become available much earlier than you would have found them in original World of Warcraft.
Beta from raids has also shaped the decisions for launch. Feedback from the community brought up some concerns about classes and the way increasing health for raid bosses and other spawns might reduce class diversity in order to be viable. Specifically, some were concerned that with warriors and rogues, not having to risk running out of mana could make them better in the longer haul that the bumped up challenge means.
During the beta test, groups that did have warriors and rogues overrepresented actually seemed to have a tougher time than those groups that were more diverse in terms of class. Ultimately, despite some of the concerns being heard, and valid, they’re not going to look to balance classes for this mode. The point of bumping up the health of the raid bosses and making things more difficult is in response to the itemization of gear and getting better items earlier. So, while they are open to changes depending how things go, this mode is intended to see players adapt in a different way than they’re used to to the same raid content.
Blizzard also answered an important question, given that Season of Mastery is intended to last for a year. What will happen after the year is up? They plan to let people permanently transfer the character they used to an existing Classic era realm for free. More details on that will come in the future.