Overwatch may indeed be the first FPS game created by Blizzard, but with creativity and totality they can create a different FPS game and quickly define their own games among other FPS games. Overwatch success continues through content updates that are constantly being offered to players. And now Overwatch is still in its heyday. It seems that Blizzard does not want to lose momentum to create another FPS project. With the difference, this new game will have additional vehicle features that can be ridden during a game may be like a Battlefield.
This information is arguably legit as it appears through job listings posted on Blizzard's official website. Where they are looking for a Senior Software Engineer devoted to gameplay and vehicles for projects not yet announced by them. In the description they also write that the position will be responsible for making the vehicle and handling the vehicle that will be used for their new project.
No other information can be found from Blizzard's latest game, although there are many theories that this game will be a spin-off from Starcraft or Overwatch, or indeed a completely new game. Moreover, it seems this game is still in the pre-development period where they are still collecting members who will work on the game. So do not expect to know the title or even the announcement from Blizzard. Because most likely we will get new information about this game soonest in 2020.