The Call of Duty: Modern Warfare 2019 campaign is the most talked about mode in Modern Warfare considering we've yet to see any information about it in the public space. However, we're now expecting to see the Modern Warfare 2019 campaign trailer before the Call of Duty: Modern Warfare 2019 beta goes live on the 12th September; this is because of a recent Twitter conversation between Call of Duty fans and an Infinity Ward employee.
Campaign Trailer Coming Soon
It goes without being said that this is extremely vague and doesn't necessarily answer the question asked, but its rare that a conversation like this would be had (even as a joke) without there being something behind it. We're not far off the Modern Warfare 2019 beta and the full game release is next month. It wouldn't be naive to assume we'll hear something soon.