As long as it's optional.
Sounds like a half decent idea actually... They've even recognised people do get up at times and leave the room while still listening, so it sounds pretty good.
I think this is about the 2nd thing in my life I've ever thought was a good idea from Sony. And I agree it should be standard, especially on the bigger power hungry TVs. As long as the user has the option to turn it off if it's not working for them (say if they have a cabinet that blocks the sensor or watch from too far away for it to see them) that is...