I apologize that I don't have a simple specific change to offer; my criticism is of the underlying basis of the narrative.
The idea of southern states seceding successfully is absurd. The shenanigans that under-represent BIPOC voters in those states disappear when you trade the ballot for the bullet, and militia LARPers are in for a rude awakening when confronted by veterans of the US military's long history of recruiting minorities to fight their wars. Thinking of 'the South' as a monolithic culture, and white confederate culture as representative of that region is reductive and wrong. If you have to write a scenario that implies ethnic cleansing into your world building, a white racist attempt leading to a Fire on the Mountain situation seems much more plausible. The people of Atlanta, Birmingham, and New Orleans would not leave behind their hard-fought civil rights without a fight.
The proliferation of the North Virginia Battle Flag in rural Indiana points to the real significance of southern secession fantasies. Renters in Austin and in Philadelphia are more similar to each other politically than they both are to home owners in Dixon, IL and Angola, LA. There's no such thing as "Red" states and "Blue" states, those are merely symptoms of a much deeper divide between urban an rural people, and a product of their relative demographics within states. This tension isn't unique to the United States and white supremacy; you can see it in the dynamic of Shi'a fundementalists in rural Iran brought into cosmopolitan Tehran to staff the morality police, or rural military units that were mobilized to massacre the 1989 movement after the Beijing commander refused. One can look at the decline and fall of Rome and the Bronze Age collapse as evidence that this tension dates back to the oldest Polis in existence.
It should also be said, the urban side of the divide has not always been the progressive force. The Kentucky foothills were once a hotbed of labor radicalism, Abraham Lincoln's anti-slavery politics were typical of Illinois homesteaders, and Welsh miners eagerly aligned with the LGBT community to resist Thatcher's capitalism.
Drawing the balkanization of America based on modern state borders is an easy shorthand to create fictional lands based on facile stereotypes of those states, but I feel there's a missed opportunity here to do something more interesting.
For example, why not replicate the overlapping zones of the historical lands of indigenous peoples? It would be interesting to imagine a world where colonialism was a brief aberration in the millennia of stewardship of the land by people connected to it rather than exploiting it. To the plains people, for example, the story of petroleum civilization is told in allegory as a great fire that burned everything, but like the grasses of the prairie, the roots of return were too deep to destroy. A side effect of building lore on this base would be to familiarize your players with existing tribes and educate them on whose stolen land they live.
Another way of drawing world maps could be based on watersheds - in a region where states no longer exist, people still need to coordinate over land and water management. Instead of historical state lines, borders that still have importance are those drawn by nature. This may be inconvenient for splitting the familiar North American map into equal(ish) parts, but the largest zone, the Mississippi/Atchafalaya River Basin (MARB) could be sub-divided into large tributaries and their respective basins.
One of the advantages would be familiarizing your players with watershed geography, and their associated ecology. Instead of viewing land as calcified states, it might be more interesting to divide land into biomes, and familiarize them with the plants and animals they're likely to encounter there.
It would also be an interesting exercise in imagining a post-state world, and how non-state organizations would operate and interact in that milieu. For example, the MARB council and the Pueblo of the Gulf could either coordinate or feud over the Delta they both claim stewardship over. How does the PG feel about the spaceport on the Nizuc peninsula? Does the launch debris safety committee of Nizuc Spaceport and the Guanahatabey Space Elevator in the Moon-Set Mountains have a cooperative relationship with the Pueblo del Golfo?
You could also use this structure to explore the theme of tension between urban and rural. For example, the watershed management councils would have to navigate the competing visions of large and populous arcologies at the river forks and the sparsely populated but upstream river highlands. How would this organization mediate between the interests of the two groups? If it was directly democratic, would the highlanders feel politically impotent compared to the more populous lowlanders? How far would the river people go to enforce their vision of water management on the culturally distinct stream tenders?
I love some of the work you've done to imagine a better future in this game, and I realize this is a large departure from some of the already established lore. I do think it has merit, as it not only envisions a better future, but also serves the meta-purpose of giving your players information that may be useful in building that future outside the game.