Matt Compton observes that semi-optional federal programs are not a new idea in American politics:
Medicaid, for instance, is an opt-out program, but no state has ever chosen to take that step.
Federal highways are also an opt-out program, but we all follow the same speed limits.
To be more precisely, Medicaid and federal highways are, like a lot of federal K-12 policy, structured around conditional grants. The federal government makes funds available for certain purposes if states do certain things, and the states can choose not to do them. In the case of Medicaid I believe that Arizona actually held out for a long time before implementing the program. And to the day, the extent of the Medicaid benefits offered from state to state vary a great deal.
The “opt-out” structure of a public option would work differently since there wouldn’t be a net transfer of tax money involved. But for the federal government to enact a policy that works differently in some states than in others wouldn’t be a breach of any time-honored principle of government. What’s more, my strong suspicion is that a public option would either be poorly designed & implemented and flop, or else if it works as intended rapidly become available almost everywhere.