World of Warcraft Shadowlands features a linear story, but those who level can skip it if they wish thanks to the Son of Destiny. This new leveling system allows players who have already reached level 60 and completed the campaign to bypass the story on their other toons, but there are a few caveats.
The Threads of Fate is unlocked after completing the story and reaching level 60 on at least one character in Shadowlands.
Once you reach level 60 and complete the leveling campaign on your first character, you will unlock the Threads of Fate feature for your alts. This system allows you to choose your alliance immediately after signing up, and it will mark the campaign as "complete" for that character. However, there are a few wrinkles you need to be aware of before choosing Threads of Fate.
All characters will need to complete the introductory quest chain for Shadowlands in the Maw. This means heading to Icecrown, creating the portal to the Shadowlands, and then escaping the Maw. It can be done in about 30 mins to an hour, but it's a bit difficult to repeat the whole sequence over and over over several alts.
Once you escape the Maw and arrive in Oribos, time will freeze and you will be greeted by Fatescribe Roh-Tahl. This is your first opportunity to select the Threads of Fate, but you are free to replay the scenario and participate in the Threads later by returning to Oribos and speaking with the Fatescribe. That said, choosing the Threads of Fate is a permanent choice in Shadowlands. Whether you choose it after escaping the Maw or later, you're locked in. Because of this, you will be prompted to type the word βFATEβ to confirm your selection, and attached is a disclaimer that your choice is final once you click Accept.
The Threads of Fate system isn't a bad way to level alts, but as of release, it could use a little tweaking. Picking your Covenant early means you'll have access to your Covenant abilities out of the gate and can farm Anima as you level up. You'll still need to reach level 60 before unlocking renown quests, soulbinds, and other late-game features, but that's a start. You will have access to world quests, all main side quests will be marked on your map and you can visit any area you want. Dungeons remain level limited, but these and PvP can be used to level effectively. The tuning issue is associated with bonus objectives: currently they take too long to complete for the rewarded experience.
If you're looking to level as fast as possible, the story is still the most effective route. Keep in mind that if you reach level 60 while playing the story, you will be kicked out of Destiny's Edge. This means that the most optimal way to level is to stick with the story until you're level 59 and close to 60. Before you start this last time, head to Oribos and turn on the Threads of Fate, then complete your upgrade. You'll skip whatever story quests you had left and go straight to the end of the game. That said, repeating ad nauseum story gets old pretty quickly, so if you don't mind the slower leveling pace, give the Threads of Fate.