I assume at least William and Connor are going to be in the show considering they were kinda the "main three" of the team in the first place, particularly William is an important person to Mia and the tech support, but I haven't heard any word on it. Zoe is currently dead, however, the future timeline has surely changed a lot now that FTA has visited the past that I wouldn't be surprised if she came back. Though I wouldn't be surprised if they kept JJ as either the main villain or side antagonist for Connor to face off (like how Anarky was for Thea), too.
I'm guessing that no word on this has been said. We don't really know anything about it except it'll star Mia, Dinah, and Laurel.