All of the casters except for Warlock got their own unique animation suites in Legion, which included new class-specific animations for their combat idle stance, precast, casting, channeling, and various left/right hand instant cast animations. The warlock animations were said to be coming at a later point.
Well, they're in the files now, and have been visible on the wowhead model viewer for months, but for some reason remain unimplemented as of the most recent beta build, except for the precast and cast animations being used for Hand of Gul'dan and Demonbolt.
Here's the new combat idle stance, currently going unused. You can view the others in the wowhead model viewer / dressing room under the "LocReady" prefix. They've got precasts, channels, and even a unique summoning animation that I assume is meant to be used when you summon demons.
I'm not sure if they're perhaps technically unfinished, or if they'll in fact be activated in the 8.0.1 live build, or if Blizzard just forgot to hook them up in-game for some reason, but they're not active in the beta and the patch is two days away, so I thought posting this here would maybe raise awareness.