The amount of mitochondrial DNA is tiny though (~0.1%, according to the article), and not particularly unique to any individual, since it is passed down lately

The amount of mitochondrial DNA is tiny though (~0.1%, according to the article), and not particularly unique to any individual, since it is passed down lately unchanged apart from the occasional mutation. There's no point having 3 biological parents unless there's a bad mutation in the mother's mitochondrial DNA.