I personally think that the incentives under a market anarchy would lead to widespread voluntary immigration and intregration, and viewed in the long-term this will only intensify over time. To be sure, there would still be some separatists on the margin, but they would effectively be ostrasizing themselves from the benefits of society to point where it would be quite economically crippling to be a racial separatist. The Hoppean's cultural cause does not play out in a real market anarchy.