Use Williamson County, Tennessee as an example of why this wouldn't work. It's wealthy and overwhelmingly pro-free trade, but it's also deeply conservative on social and cultural issues. In real life, that makes it an extremely safe Republican county, but in this world, these people would have no party to vote for.
Such a place would become a swing county. Voters swinging back and forth based on which set of issues dominated and the economic backdrop.
Do you think there aren't counties and groups of people that don't fit in the parties right now? Why would it be so shocking for that to shift to a new type of counties and voters?