Honestly, I fully expect the next expansion to break the pattern and forego a new class. My expectations for BlizzCon were tempered by last year’s, to say the least.
That being said, Tinker, I’d be fine with, if not surprised that they chose to go with that theme for an expansion.
Dark Ranger would be disappointing. They’re a very specific fantasy - Elven, dark and brooding. I don’t think we need another one of those. They’d probably make for a better Allied Race, but even then, the concept is still too narrow.
WoW’s draconic lore reliably results in strong thematics, and can have incredibly strong stories to tell with the right writers. Dragonsworn would allow us to tap into that fantasy, and give the developers a lot of creative freedom with the design.
Also, to those above, a Warrior is inherently no more a Dragonsworn than she is a Paladin or Death Knight. Nor is a Mage no more a Dragonsworn inherently than he is a Warlock or Demon Hunter.
Aside from a few abilities being draconically themed, the full fledged fantasy of utilizing that draconic power fully is not represented at all.