In an interview, Blizzard revealed that “Heroic Week” is returning in The War Within.

Dragonflight changed the raid release schedule for the first time in a while, removing “Heroic Week” — a one week period where Mythic raids and the full loot pool of Mythic+ were not open. While removing “Heroic Week” had upsides for certain players, such as not having arbitrary caps for 1 week, it has been criticized by others for:

• Having guilds feel like they have to spend every available hour doing Mythic+ spam on the first week in order to get geared up for Mythic
• Raid bosses having a larger power delta between the first and last Mythic boss because of the lack of Heroic Week
• Lack of Class Tuning from data collected on Heroic week
• The first couple days of Race to World First being nothing by Heroic splits

In a group interview with Michael Bybee, “Heroic Week” is coming back to The War Within!

[…]To be a little bit more specific here. One of the considerations for the War Within is, for the first time in World of Warcraft history, we are doing an early access period for folks who are able to purchase the higher end product, and so they’ll get 3 days early access for that. One of our very major goals with allowing that was that it didn’t feel like it gave folks an advantage, especially in any power race. So that 3 day early access will give folks the ability to play through the story content, level up, get to max level but they won’t have access to a lot of the Mythic 0 and other opportunities where they can get sets of gear. Then we’ll have a period where we’ll actually have access to the Mythic 0 system without the Season having gone live, then the Season will start and you’ll have your Heroic Week and then you’ll have the rest of the content unlocked.