A source close to the development of the new Red Dead game has now confirmed to us that the map is indeed the real deal, revealing that this is a "very recent" art direction map for the upcoming title.
They also confirmed that the game will be set before the events of Redemption, and that the new map is just east of the one that featured in Red Dead Redemption.
If you look at the bottom left (click to zoom) you'll see the Great Plains, home to the Blackwater settlement that sits at the top right of the Red Dead Redemption map - so you can see how the two come together. The lack of a railroad in the Great Plains, which featured in RDR, also points to this being earlier in the timeline.
Thought the colors looked a little pukey, so I tried just black & white. Easier to read now!