A new gameplay video has leaked via Reddit, which shows off early footage from Call of Duty: Black Ops 4 and interestingly shows off a campaign mode that didn't make it to the final release.
Posted by redditor ForeverDexus, the campaign would have seen you attempt to extract a CEO from a hostile situation. While it's certainly far from the polish you would expect from the final version of the game, it seems reasonably far along in development.
The campaign was going to be 2v2, and not a single-player campaign, though. You can see some minor differences between the gameplay experience in this and the final version of the game, however, and players would pick different factions and compete against each other.
Treyarch has stated previously that Black Ops 4 never planned to have a campaign mode of any kind, although clearly, this was never the case at one stage in development. It's an interesting insight into the development of the game, for sure.