It was fairly obvious from the trailer what he was about (see how that works?) His age and obviously Jedi training aside; he has a padawan (braid and all), plus the headset she was wearing in the fighter is literally the same prop from AotC & RotS. That means it's Jedi issue. That and the not-red blades all pointed to an Order 66 survivor and his apprentice.
What they're trying to do and how that intersects with Thrawn & Ahsoka's stories remains to be seen.
Really? Its literally been over 30 years since 66. Have something else.. Like Vader trainee or emperors hand. Not every force user us a 66 survivor. Its getting old fast.
Uh, where do you suppose a "Vader trainee" or "emperor's hand" would come from? By sheer necessity they're either going to be Jedi that have been turned one way or another, just like the Inquisitors (who BTW are by definition also "Order 66 survivors".) Force sensitivity to a degree worth training is rare to begin with. Training in the Jedi/Sith arts even rarer, and that was back when the Order had cornered the market on that kind of thing. After the Empire, people capable of passing on that knowledge are vanishingly scarce. Probably as few as a hundred people, scattered across a galaxy of quintillions, and most of those never made it past the rank of Padawan, and have zero desire to go anywhere near a lightsaber ever again.
But OK, for the sake of argument: If the goal was simply to have an antagonist that can use the force, then for sure there's multiple options. From Sorcerers of Tund, to surviving Nightsisters, to Mara Jade, or even Starkiller himself. However, I suspect there's a specific purpose behind this choice.
As any good nemesis should be, I suspect these two meant to be a dark reflection of Ahsoka's own history. A
"there but for the grace of Dagon go I" set of characters. In another world, another time, that could have been her and Anakin, or Kanan and Ezra. Not Sith, but a living embodiment of the failure of the Jedi. Not necessarily fallen to the dark side, but still lost and blind to the light. Fighting because that's all they know how to do anymore. Soldiers, where they should be keepers of the peace.