southwestern states see mass enfranchisement of previously undocumented immigrants and new power structures emerge as a result,

More likely, instability, cartel intrusion, and ethnic cleansing causes a mass-exodus.

middle states control the nukes, food and water and so become disproportionately influential despite their low populations,

More likely, the removal of agricultural subsidies and continued deindustrialization decimates the region. Neo-Nazi meth cartels and Evangelical cultists rule the region.

reservations become independent states which generally allows them to improve their conditions, but lack enough economic or military leverage to influence the other states around them,

Maybe the start down that path, but they'll likely be in conflict with the state governments. Being completely surrounded, they likely won't last long.

the new military hegemon of the Atlantic becomes the Confederacy, which inherits most of the military community and hardware of the previous superpower, but with most of the FBI/CIA types remaining in the northeast it is unable to effectively repress its African-American population for very long and is eventually taken over by them.

I'm picturing a New York technocrat allying with the EU and Canada to continue the NATO project, but with a limited scope.

Neo-Confederacy will see racial tension, but the Black population is a minority in every state. Maybe they'll form isolated rebel communes, but never a recognized government and never over the whole region. Also, it's likely more will move up north.

You're right about Texas and California. For Hawaii, I think selling the navy outside the US will be controversial. Probably California takes over the Pacific.