I don't think another secession will happen any time soon. Americans are too fat and happy to want major changes, and that's fine. Also, the devastation of the Civil War is still too fresh. However, it would be foolish to believe the United States will remain unchanged indefinitely. At some point in the future, the United States will either join a larger confederation, suffer invasion and subjugation, or splinter into smaller nations.
History marches on.
I personally believe secession has a good chance here within the next century. Further, I think secession might be the best development for human liberty since the Revolution. Therefore, I believe it's important to keep the concept of secession alive, and to defend it against detractors. As I noted in my last article, my preference is to return to the loose federalism described by the Constitution. However, there's a reason that document failed to reign in the national government.