That's according to Polygon's sources, so who knows. But it sounds like this might be the first game in the series to ditch a SP campaign entirely:
The sources, who asked for anonymity, said that as Black Ops 4’s release date approached, it became evident that development on the single-player campaign wouldn’t be completed. One source said Treyarch has since focused Black Ops 4’s development on expanding multiplayer and the series’ popular Zombies mode. The source described an emphasis on cooperative modes as a potential stand-in for the typical single-player campaign experience.
Maybe it'll have a short campaign (although they're all pretty short to begin with)? I can't say this affects me much, as I don't really buy COD games anymore (the MP doesn't appeal much to me and while I generally enjoy their campaigns, they never quite hit that 10-15 dollar mark on Steam that would make them impulse buys). But it'll be interesting to see if it affects sales at all. I'm sure Activision knows precisely how many people start a new campaign rather than just jumping into multiplayer and I doubt it's that many.