[aeorgnoieang]

> In the software world, we would fork or rewrite, and deprecate the old version.

Yes and no. Can you name even one specific example of this being done with software on a scale within even an order of magnitude of "healthcare"?

Certainly people fork and rewrite software all the time. But almost all of those projects fail to replace the 'old version'.

And even large software projects that are rewritten are often (heroically) written so as to be (maximally) compatible with the ecosystem of users.

> The only obstacles are political and legal, which can be overcome in one or two election cycles.

This is both wildly optimistic and pessimistic. Vermont voters passed a single-payer referendum (but the government decided to cancel the plans because of the estimated cost). I'm not sure that there's much of anything stopping a single city from doing so (besides things like free-healthcare tourism).