I'm thinking make Thrawn fast. Offensively you can swap TM with another character... defensively he will most likely fracture the other teams auto taunt.
The rest of your team I wouldn't worry about speed as much... intentionally make DT on the slower side to dispel all the hot's, tenacity etc that a triple cleanse team will put up trying to dispel the fracture. The others on your squad should fall right behind DT... of course hits to Krennic if you run him could throw a wrench into that by giving DT TM and allowing him to move before all the opposing cleansers go... all the TM boosts from Thrawn lead (especially with characters like ShT or veers on the team) will help justify dropping some speed.
Unless you run Thrawn as lead I'm thinking you will still want a cleanser like Kenobi...
I like the idea of Krennic lead... but as it stands it fails pretty miserably in arena and I'm not sure Thrawn will help enough to make it viable...
Gonna be fun to play around with and tons of ideas to utilize him best... I'm excited to try him out!