I think it's useful to think of 10.0 as the anti-Cataclysm honestly. Or what they imagine Cata would be in 2023.
All the set pieces are in place.
- Wrathion is here, seemingly a better version of his father.
- The Dragon Aspects seem to be relevant again.
- Hints of a world revamp.
- Devs mentioning a return to basics etc.
- Rumblings in the lore about future threats from the Void.
Deathwing broke the world in Cata, and the Dragon Aspects lost their powers. I think Wrathion will help rejuvenate the world in 10.0, and the Dragon Aspects will regain their powers (or gain new ones).
The Dragon Isles could be a new continent, but it could also be a small endgame patch zone, or zones simply built into Kalimdor and Eastern Kingdoms like Uldum and Twilight Highlands in Cata. Or they could be some sort of mini-hub for people who follow a certain Flight. Like, all devotees of the Green Flight gain access to a "green dragon island", which could either be a pocket-dimension inside the Emerald Dream or a literal island somewhere in the sky. But instead of a full zone it could be where such players meet up to collect rewards, pick up quests, interact with various systems etc.