Farkel:
I agree that it is unlikely that the U.S. Supreme Court would ever hear this appeal. First, the California Supreme Court would have to agree to hear it, which is a discretionary appeal. Even if that happened, only about 1% of cases appealed to the U.S. Supreme Court are actually heard by that court. But the test for whether it can hear an appeal from a state supreme court doesn't have anything to do with the 10th Amendment. The test is whether the case meets the requirements of a federal statute, 28 USC 1257. The case must also meet the requirements of Article III of the US Constitution.
Since punitive damages are involved in this case, it is possible that these would be grounds for appeal to the U.S. Supreme Court. They have heard state-law cases involving punitive damages in the recent past, such as State Farm v. Campbell. The theory is that the improper award of punitives or excessive award of punitives can be a violation of due process, which is guaranteed by the U.S. Constitution. The Watchtower could argue that awarding punitive damages for the purposes of forcing a change in policy is a due process violation, and that would be grounds for the U.S. Supreme Court to hear the case.
So, that's my amateur roadmap to how the U.S. Supreme Court could hear the case. I think it's extraordinarily unlikely, but not impossible.