Remember "Band in a Box"? This seems similar to that, except this appears to fill in a harmony based on the melody of your voice.
Band-in-a-Box goes way beyond what MS is doing. BIAB is a marvelously useful app for music composition education. It also has sufficient depth that it frequently finds a role in professional settings.
But BIAB's best feature (and biggest selling point) is that it's fun
to play with. I think Microsoft realized the importance of that when they created Songsmith.
After looking at the advert video, I wouldn't be at all surprised that MS is licensing some of the technology used in Band-in-a-Box.
P.S. I don't know who wrote that ad, but whoever did really needs to get out of marketing. I have seldom sat through something quite so painful as that. One minute into it and I was actually cringing with embarrassment for the actors. Hope they got paid well.