Yes, certainly the power structure has changed, especially as regards the federal government vis-a-vis the states, but I'm not sure that that power differential has shifted in favor of the states since the 1860's. Beyond that, there isn't a state in this country in which a majority want to quit the United States.
I had never heard of these brave folks who went to Brazil. I have a lot of respect for them.
What you say is true, however, sentiments change. And they’re changing now as is evidenced by the petition drives and the discussion of the subject.
Few people in 1760 would have bet that the American colonies would divorce from Britain less than 20 years later.