Call of Duty: Black Ops 4 made the decision not to feature a single-player story campaign. Instead, it included the series' traditional multiplayer content, as well as the new battle royale mode, Blackout. However, there's a chance that not all of the games in the franchise will ditch single-player moving forward.
According to job listings by developer Infinity Ward, which is currently working on this year's Call of Duty game, the qualifications for an associate game designer states that the developer wants candidates who have, "A broad understanding of both multiplayer and single player game design." The hired game designer will be working with other, more experienced designers on "creating and implementing new game features."
There have been rumors that Call of Duty 2019's single-player campaign will just be a remaster of the one from Modern Warfare 2. However, the qualifications for the associate game designer also call for candidates to be able to "dissect and discuss level design in recent games." Unless Infinity Ward plans to drastically overhaul the single-player levels from its 2009 first-person shooter, it would seem odd that it requires candidates to possess such a skill.
The apparent confirmation that Call of Duty 2019 will feature a single-player campaign isn't the only morsel of information included in Infinity Ward's job listings. In a separate post for the role of senior gameplay animator, the studio says that job duties will include working with the rest of the development team to "set a new bar for 3rd person player animation in a shooter." Call of Duty is known for its first-person gameplay, and it's tough to imagine that Infinity Ward would make such a big departure from that. Nevertheless, it may well make that jump if it wants to do something ambitious.
It's also worth noting that the job listings for both the associate game designer and the senior gameplay animator refer to this Infinity Ward game as a "next gen title." Other job listings from the studio have indicated that Call of Duty 2019 will be released on next-generation consoles, but these listings just pour more fuel onto the flames. Rumors have been heating up in general about when the next generation of consoles will be announced, but this suggests that the new consoles could be released this year and that Call of Duty 2019 would be a major launch title.