It looks like our early thoughts on the announcement were correct, this is Far Cry: New Dawn and much like previous titles in the franchise it will be a spin-off to Far Cry 5 rather than an actual Far Cry 6.
We saw this with the last couple of games when Ubisoft gave us the outstanding Blood Dragon and Primal. Both a change from the normal game but so much fun and bold in content choices.

New Dawn will take place seventeen years after the nuclear devastation witnessed in Far cry 5’s Hope County, Montana., The area has changed significantly in unexpected ways.
Nuclear winter has given way to a “superbloom,” creating a lush, colourful landscape that survivors have begun to re-populate with makeshift buildings.
It’s a lawless frontier where people are struggling to get by – and you’ll be able to experience it all with a friend in co-op, or on your own as a lone gunslinger.

The locals have a new threat, “The Highwaymen”. These are post apocalyptic scavengers that as you would expect look a bit like something from Mad Max. They are led by the games antagonist “The Twins” who we saw on the games cover design.

The Twins are named Micky and Lou and have grown up in the harsh harsh new world learning to survive by any means necessary. For them, there is no tomorrow – only the present and that creates a chaotic enemy.
The description of the game makes it seem like it’s a world that has reverted to an old west mentality, or is that me hoping for a game that not only can teach Fallout 76 a few lessons in graphic progression and gunplay but may also itself take some story concepts from AAA titles like Red Dead Redemption 2
Far Cry: New Dawn will be available on February 15th 2019 on Xbox One, PS4 and PC.
Read more about it from the source: https://far-cry.ubisoft.com