Just spitballing a few ideas here.
Concept: Historically, the dragonflights would imbue a select number of loyal mortals with a tiny bit of their power. The most well-known members are the Druids of Ysera, although there are examples from all dragonflights employing these devout mortals. Given the inability for the dragonflights to procreate, the need for these loyalists has drastically increased in recent years in order to keep their respective spheres of power in check.
Three Specializations:
In general, Dragonsworn classes require more positional awareness than other classes to thrive in their given roles. Ideally, I would have liked to see them fulfill more of a support role, but given that WoW has long since moved away from that particular facet of MMO gameplay, I thought of something a little unique.
Melee/Ranged DPS: Taking a page from FFXIV’s Red Mage in reverse, the Dragonsworn DPS class builds their draconic power in melee range before leaping back to unleash powerful magic and/or breath attacks. Many attacks have movement built-in, and managing your spacing and position is required for an optimal rotation. Talents are available to viably create entirely ranged or melee builds, although positioning remains a focus of any Dragonsworn.
Positional Tank: Thriving when in the thick of battle, interesting options present themselves depending on the relative positions of the enemies to the tank. A breath weapon/tail thrash ability might require at least one enemy in front and another behind, whereas a powerful ranged AoE has a lengthy minimum range.
Fixed-range AoE Healer: While more traditional options exist, the Dragonsworn healer thrives when he is able to toss out fixed-range AoE skillshots. Lobbing a cleanse onto a tightly packed group of DoT’d melee, using a healing breath lined up perfectly with ranged, melee, and tanks.
Available Races: Dragonmaw Orcs and Wildhammer Dwarves. Both masters of the sky in some form, and both reeling from recent losses, these denizens of the Twlight Highlands have dedicated themselves in full to the dragonflights to once again establish themselves.
Unique Gear: The “back” slot adds a myriad of draconic customizations, including scales, spikes, tails, horns, and wings. Different specs have access to different options.
"Flavour" Choice: Players choose, soon after creation, which dragonflight they will dedicate themselves to. This is primarily to inform aesthetic options available to the player, and to give unique animations/colourations to certain spells and abilities, but also affects the story in minor ways.