I really would be surprised with a Dragon themed class tbh. Honestly I'd rather the main theme of the xpac is shared by all. I think the best idea was the Ashes of Galakaros one; make completely cosmetic Dragonflight "covenants" give each spec an ability and just reskin it depending on people's choice of Dragonflight. Not to mention there are several Dragonsworn in lore and they are all very specifically other classes; Dragonsworn is a title more than a class.
I would not mind not getting a class. I'd rather they made a solid effort to get all or at least more specs to feel good like they did with Legion (and mostly managed by the end of the xpac) and would definitely prefer class customization the most. I'm a TRPG player and I am used to having tons of classes. In a TRPG setting I could see WoW having close to a hundred archetypes and that can be pulled off there with classes/subclasses and prestige classes. But WoW itself can never really pull that off. There are many very cleanly presented archetypes in WoW that can never really become classes; they would be too narrow and really at the end of the day there are too many of them. However if they were willing to take more risks with customization and the talent system, it's definitely possible to broaden how we play our characters without having to add many new classes. Not saying that you can't have classes added btw. Tinker is one of them were the theme is wide enough that you could easily add it. But you could just as well have engineering unlock class skins for a dozen different specs and make them tinkers instead.
Now what I think would be truly innovative if we do get Dragon Isles would be to actually see them try and use flight. One of the best gameplay features I've seen in wow in quite a while were the Mechagon back packs. I think a great way to do Dragonflights would be to give us DRAGON WINGS which would function only in the Dragon Isles and work like the backpack. Then just make sure to actually add flying threats. It can be done. TBC had so many flying threats, they did it in Zereth Mortis in the desert area. As long as flight doesn't just let you go straight up and avoid all combat it is not problematic. It would also let them make a more 3D environment and allow for the zones to be vertical or even floating! without them feeling disjointed. For me one of the worst parts of Shadowlands is how disjointed the zones are. In no other xpac did I constantly tab out waiting for a flight path. Even with Cata we had flying on day one and numerous portals so moving around was easy.