[Update #2]: World of Warcraft's Shadowlands expansion has been pinned for an October 2020 release date!

[Update]: The Shadowlands pre-patch has landed onto the public test servers alongside the leveling rework, class changes and new event!

As you're likely well aware, World of Warcraft's Shadowlands expansion will bring with it a comprehensive rework of the leveling process. Not only will you be able to freely choose which expansions and zones you'll adventure through, but the whole ordeal will be significantly faster than it currently is.

While this is certainly a positive change, the newly increased leveling speed does leave Heirlooms (account-bound items that increase experience gain) in a bit of an awkward spot. So in order to find them a more interesting niche, as well as to stop them from essentially being mandatory, Blizzard has now announced that they are planning to have Heirlooms feature set bonuses in Shadowlands.

You can find their current iteration right below, though it is worth mentioning that Heirlooms are still a work in progress and a very likely going to undergo major changes by the time Shadowlands rolls around. With that said, here's what Blizzard has cooked up:

(2) Set: Rested experience consumed is reduced by 30%.
(3) Set: Increases your out-of-combat regeneration in the outdoors, normal dungeons and battlegrounds.
(4) Set: Gaining a level triggers Burst of Knowledge, dealing Holy damage to nearby enemies and granting you 40% primary stat for 2 minutes. Defeating additional enemies extends this effect, up to 2 additional minutes.
(6) Set: Rested experience consumed is reduced by an additional 30%.

Needless to say, these aren't exactly exciting effects. In fact, they look more like placeholders than anything else, so I have absolutely no doubt that many of them will be changing over the coming months. Personally, I can only hope they'll make these set bonuses offer fun quality-of-life improvements over raw power, because getting things like movement speed after each kill would be far more enticing than simply dealing 5% more damage while leveling.

Either way, you can learn more about Blizzard's plans for Heirlooms in Shadowlands over at the WoW forums.