I always heard “another thing coming” until sometime in, say, the last twenty years. I took “another think coming” to be a variant people employed to be funny. Since I am not much younger than Rand Simberg, it may have once been a regionalism to use think rather than thing, so we learned it differently when young. It’s unfortunate that noting the difference was lent emotional attachment by deploying it as Sarah-bashing, thinking she’s stupid for using the more common version of a phrase.
On the plus side, from the comment thread I learned that “another think coming” was the original, largely replaced by morphing of the language.
That’s even more than Obama’s 57 states! This is an amusing and intriguing hypothetical map experiement showing what the US could look like had all secession movements succeeded. Clearly there is more to it than that, to make Cuba a state, for instance. And we gained some from the present Mexico, but Canada not so much.