With advanced surround sound via technologies like Dolby Atmos and DTS:X, these would seem like somewhat of a "dated" idea. Not saying that the mass population is going to an Atmos or DTS:X configuration, but putting the surrounds up in the corners and pointing them down wouldn't work well with in-ceiling speakers in almost the same audio plane.
Also, when ignoring the newer formats, the ideal placement is down closer to ear height, so while the product could find some usefulness for a few customers for esthetics, I think that the mainstream user would rather have something more sonically accurately located.
With all of that, I do think that it is a cool idea and would hide the speaker location better than on the wall, and heck it would be good for an Auro 3D setup (not that I think Auro 3D is going to get very far), it might not see enough customer need to justify a product creation.
