Theft will be added in Update 9.1 after completing the Shadowlands Pathfinder achievement.
Like the aforementioned expansions, flying in World of Warcraft Shadowlands will require the completion of the Pathfinder achievement. This means fully exploring each area and completing all the quests within it, but you will no longer need to reach Exalted with the major factions for success. That requirement will be replaced by Renown according to executive producer John Hight (in a since-deleted interview with HazelNutty on Twitch).
We don't yet know what specific Fame Rank we'll need to achieve, and there's always a chance it will be a Fame Rank added in Update 9.1. However, it's much easier to grind and catch up with fame than reputation, so it's a welcome change. As for knowing that theft will come in patch 9.1, and not the second major patch for Shadowlands (which has been the norm for some time now), this tidbit has been confirmed by Ion Hazzikostas. In an interview with WoWHead.com, he said the flight will debut in Shadowlands Patch 9.1. He also confirmed in that same interview that the Flight Master whistle will not work in Shadowlands, and we've been feeling the loss since launch. Go Blizz, add more flight points to Bastion!
Since it takes around 4-5 months for the first major fix to be deployed, now is a great time to start taking down your Pathfinder goals. Success may not be in the game yet, but exploring areas and clearing all side quests will be prerequisites if previous Pathfinder achievements are needed. Work on those two things and complete your weekly fame quests to make sure you can fly as soon as possible after patch 9.1 launches.
