I know it's been done in mice but I don't know how efficiently, although these days the main way you transform mouse germline DNA has been doing low-efficiency transformation and selection of embryonic stem cells in culture followed by 2 generations of mucking around making chimeric embryos from those stem cells and breeding the resulting animals so this definitely saves time if it works well.

If you can do it in one generation that also means that you can start doing it in humans embryos.

For legal reasons probably not in the West, but I can imagine that the Chinese are willing.