There has been talk around the 'internets' that suggest Call of Duty: Black Ops 4 could end up being a Battle.net (now known as Blizzard.net) exclusive. While Activision themselves have not yet made any official statement behind this, the truth is that the company made this move with Destiny 2. While the first Destiny skipped PC altogether, the sequel was only launched on Battle.net - the first non-Blizzard game to do so.
Now, according to a source that reached out GamingIntel, Call of Duty: Black Ops 4 might follow suit. This source shared pictures of what is supposedly a beta version of Battle.net, showing Black Ops 4' logo next to Destiny 2 logo, and claims Activision goal is to turn Battle.net into the exclusive PC platform for all their games, much like Origin for EA.
Again, none of this has been officially confirmed, or verified by other sources, so take it as a rumour for now. It is a rumour though that makes a lot of financial sense for Activision as they would no longer be forced to pay 30 percent off the top to Valve. The counterpoint to that is naturally a decrease in sold copies...
We'll no doubt learn more about this in the near future.