Population genetic studies that are designed to capture pre-historic genetic diversity and the origins of modern "peoples" focuses on "pure blooded" individuals whose ancestors (typically at least back to four grandparents) have known and identical origins in the locale to which the sample is assigned. There are studies of admixed populations (e.g. mestizos and African-Americans, the people of Madagascar and "colored" Anglo-Caribbeans and South Africans), but those studies usually focus on populations where the admixture was population-wide, took place half a dozen generations or more ago, and may have involved considerably less of a choice element than is found in modern mixed couples.
For the purpose of discerning pre-historic population structure, this kind of selection makes sense.
But, it would be interesting to see, from a genetic diversity and heredity perspective, if there are systemic differences between monoancestral people and multiancestral people, in general.
For example, are there genetic trades related to psychological makeup (e.g. traits linked to the Big Five personality trait of openness to experience, or traits linked to novelty seeking) that are found at markedly different frequencies in monoancestral and multiancestral people?