I'm not a fan of Drakonids as a playable race. They would look awful in any gear that's not designed around their skeleton and there's very specific reasons the Dragonflights stay neutral to the Alliance vs Horde conflict. Hell they've been a majorly prevalent enemy for a lot of the game's lifespan.
Dragonsworn probably makes the most sense to add as a Class since it's much easier to fit into existing races, although it's a stretch lore-wise as there's only anecdotal evidence and speculation that they even exist in WoW. The very page you linked on them says it's non-canon and all the WoW NPC's are speculated to "may be transformed dragons" or "might match the criteria for being Dragonsworn". Your example of The Timewalkers is irrelevant, none of their members are Dragonsworn, they're lead by Bronze Dragons and the rest are just sworn to defend the timeways, research or recording of events. Nothing in any of the individual members' pages mentions anything about any of them being Dragonsworn.
Dragonborne I don't really understand how you could make a class out of. You're just a regular dragon that is for whatever reason siding with Alliance/Horde. You have 2 abilities, Elemental Breath and Melee or you transform into a Humanoid and become a Warrior or something. There's no basis for a playable class here (Yes I read through your concept and it's all horrendously OP for the sake of being "cool dragon abilities"). You're also completely ret-conning what the Chromatic Dragonflight is and is capable of to justify a Dragon being able to change colours (Not what a Chromatic dragon is at all..)
"The chromatic dragonflight of Blackrock Spire was created by Nefarian's magical experiments, using the blood of dragons from the other dragonflights.[1] These experiments were largely considered failures; many whelps died before hatching, and those that survived were unstable, short-lived, volatile, and/or deformed.[2] Those that reached adulthood were artificially aged by Nefarian's twisted magics.[3]" (
https://wowpedia.fandom.com/wiki/Chromatic_dragonflight)
Doesn't exactly sound like the basis for a powerful Hero Class now, does it?