In DM, the location was fictional. In HH, the location was fact based. In OWB the location is possibly fact based, as in the Big Mt Ridge, of CA.
What puzzles me, is that the note make reference to "up north". There is no Hopeville CA. The HH DLC took 14 in-game days to get there.
The Divide could be north of Big Empty, intuitively I've always placed it as south of Vegas. Also, Big Empty was mentioned as a supply issue for NCR. Regardless, the Divide is confirmed in-game to be near Death Valley, a dreadful place with really bad weather. Hopeville is a place where weather experiments were done. In addition, High Rd. from the screenshots indicates they will likely be juxtaposing nice names with the inhospitable area. So logic follows that Hopeville is a fictional town established near or in Death Valley and is the set of the DLC.