I see many good ideas, but the most plausible scenario, if you asked me, would be a Polynesian-European culture involving a POD during the age of trans-oceanic exploration. Perhaps a fleet of British or French ships gets marooned on a Polynesian island and the castaways become assimilated into the society of the natives on the archipelago.
Then again, most of Latin America is a hybrid civilization of Spanish and indigenous cultures, so now that I think about it, this phenomenon was common IOTL.
I also wrote an AH on this site about a "Norskimo" culture. Basically, the Greenland Norse survive by integrating into the local Inuit population and from Greenland and Labrador-Newfoundland their hybrid offspring colonize much of Northeast Canada and move southward into New England and the Great Lakes region. I never finished the scenario however.