According to a job listing for a Senior Software Engineer, Blizzard are working on an a yet unannounced FPS involving vehicles. The listing, which can be viewed below reads as follows;
“Blizzard Entertainment is looking for a talented gameplay engineer to help create vehicles and build vehicle handling features in a robust first-person engine for an unannounced project”, the ad reads. “The ideal candidate has proven experience in vehicle handling, with exposure to other game systems like physics, animation, and cameras. They must have outstanding people skills and a longstanding passion for playing games across multiple genres and platforms”
In terms of what this game could be is anybody’s guess so we will have to wait until Blizzard make an official announcement, maybe at BlizzCon 2018.