Thanks! I'm a fan of decentralized democracy too, in large part because it seems to be a more stable form of government than the representative style which spawns a civil war every couple generations.
I agree it's unlikely we'll see a deliberate or managed transition, though, given how much power has condensed in D.C. over the years. The Capitol attack showed that there are probably enough people willing to fight over control of that power to produce an actual second civil war. And what would Lockheed, Boeing, Raytheon, and all the rest do without the feds shoveling them money year after year? They're betting big on Cold War 2 right now and nobody seems to be willing to question it.
Eventually I bet we'll see fragmentation, but more than likely it will be so chaotic little if any federal government is left. Possibly a shell only half of the states listen to at any given time.
What I think is really going on under the hood of everything is very natural process, a complete reordering of the US as old contradictions can't be reconciled in the same system any more. The future is impossible to predict, general scenarios are all you can produce, but these can give a general idea of how things might evolve.
The best-case outcome I can come up with is pretty much the Swiss model, with the federal government not actually directly taxing and spending much at all, but acting as a simple guarantor of agreements between coalitions of cantons or regions. Like in the EU, all members would have to follow certain rules about debt to national income ratios and resort to austerity if they mismanage the local economy, but you keep a common currency and let regions have their own economic cycles.
In return they contribute a fixed % of GDP for national-level projects like collective defense. That should mitigate the pressure for the ridiculous levels of Pentagon spending. Big businesses would lose the ability to pull one lever and affect operations across the whole country, but most are so global anyway I doubt they would ultimately find it too difficult to adapting to the 2-4 different regulatory regimes that would probably emerge across the US.
The biggest roblem with a system like this is that any hope of a national system for enforcing civil rights or gun reform is gone. But since the feds do a terrible job at that as it stands I don't know how much worse off people would actually be. All they've got to offer any more is fear of China/Russia and spending vast amounts of money we all *hope* will trickle down to help us.