I will take a bet on this, if you like. Also, did you perhaps mean "attempt to secede", or are you predicting actual success? I'll take the bet either way.
On further reflection I think I need to revise my estimate down somewhat. Thinking on it further my 30% estimate is conditional on general trends that I think are more likely than not to occur but I did not correctly incorporate them into the estimate for secession. I think 10-15% is probably a better estimate taking that into account.
I think the political pressure for secession will stem from an extended period of economic weakness in the US and widespread fiscal crises in states like California and New York. If, as seems likely, federal aid is seen to go...
I would like to propose this as a thread for people to write in their predictions for the next year and the next decade, when practical with probabilities attached. I'll probably make some in the comments.