In the 2024 Roadmap for WoW Classic, Blizzard announced that there would be at least four new phases for Season of Discovery in 2024. Wowhead has already Datamined one item from Gnomeregan, which is planned to release early next year, as well as Blizzard teasing future raids for Phase 3 (Level 50) and potentially Phase 4 (Level 60).
We've datamined one item that will exist in the level 40 Gnomeregan raid, which is a new and improved version of one extremely popular item from the Gnomeregan Dungeon. Many players will be very excited to obtain this new item, which we've hidden for those interested in not being spoiled --
At BlizzCon, Blizzard also teased multiple new raids at the end of the Season of Discovery presentation. Other than Gnomeregan which we already know is coming next, it was also revealed that potentially a Scarlet Monastey raid might exist, as well as a Karazhan Crypts teaser.
While there is an additional phase planned to launch in Autumn 2024, this would be an additional content phase for Level 60. Blizzard did reveal that they will be releasing the original Classic Raids (Molten Core, Blackwing Lair, Ahn'Qiraj, and Naxxramas), we aren't entirely sure yet if all raids will be accessible or if they will be released in phases of their own. Here is an excerpt from our interview touching on this