not really genetic modification (Score 4)

If I understand the article correctly, DNA is NOT being inserted into mitochondria. The children are not "genetically modified" in the traditional sense. The mitochondria from mother 1 had a defect, so mitochondria from mother 2 was injected into the haploid egg or single cell diploid embryo. The term for this is cybrid (CYtoplasmic hyBRID). This is a technique that's been used before when working with cell lines that have had their mitochondria killed off through exposure to ethedium bromide for ~3 months (rho0 cells). You kill off the mito, then repopulate the cell with mitochondria you want. In this case, it sounds like the children have a mixed population of mitochondria. This would mean that females could still pass the defect to their offspring.