According to Kotaku's sources, Call of Duty: Black Ops 5 will be developed by Treyarch and released in 2020 following a "major upheaval" at Activision.
While this year's Call of Duty game—which we're likely to hear more about before E3—is rumored to be Modern Warfare 4, previously Raven were the studio heading up the 2020 entry in the series, " a Call of Duty game set during the Cold War". Now that game will apparently be repurposed into a singleplayer campaign for a new Black Ops by Treyarch, which was previously on the cards for 2021.
Given how upset players were about Black Ops 4 lacking a proper singleplayer campaign, this would seem like a good sign. Something that will not likely be as well-received is what the report has to say about Modern Warfare 4 being influenced by free-to-play games. "Internally, Activision executives have started to talk about embracing free-to-play as a revenue model—once anathema to the publisher—and, three sources say, are looking into offering a free-to-play component for this year's new Modern Warfare", as Kotaku puts it.
You can read the full investigation here.