And I'm not asking rhetorically this time.
Have there been any major national programs with an opt-out clause from which states have actually opted out?
At a glance, Medicaid is opt out. But only Arizona opted out, and they opted in again in 1982. No other state has bailed out of the program. The federal highway bill had an opt out, but no states opted out of that either. And while it's not explicitly an opt out bill, a lot of Republican governors ripped apart the stimulus bill and some even threatened to turn down the money -- but, shortly thereafter, photos turned up with grinning wingnut governors holding giant stimulus checks.
Are there any other examples one way or another?
I don't think any states will opt out of the public option. If they didn't opt out of a "welfare" program like Medicaid, it's very unlikely they'd opt out of the public option.