Prior to Overwatch, Blizzard really wasn't in the business of making first-person shooter games. Now that their first venture is a total success beyond anyone's imagination, it appears they're working on a second and are hiring some people to do it.
NeoGAF were the first to spot three job listings for Blizzard that specifically deal with an FPS game. The first two gigs are for Lead Software Engineers, the first to work on a first-person engine while the second is for an "unannounced project" that utilizes the first-person engine. Both of those jobs are asking for people who have worked on those types of games before. The third is a Senior Technical Animation Artist who also needs to have experience working with an FPS POV.
Now that the facts are out of the way, let the speculation begin! Are they working on a brand new IP? Could Blizzard already be working on a sequel to Overwatch, or possibly expanding it so that the game has a proper story mode? The possibilities of what may come are pretty cool to think about, especially whether or not Blizzard will work to make a new game that rivals its own popular property or if they expand on the proven IP and make it better for years to come. In any case, the jobs are open, so if you got the skills, you should totally apply!