I suspect one of the reasons that this is now being suggested as a product offering is to save Openreach money by reducing the requirement to run as many E side copper cables seeing as their future value is rapidly falling away as more customers ditch the landline and use FTTC based services.
I, for one, am looking forward to this given that I have 4 lines and only use 1 for voice!
While this is now quite outdated... I remember years ago there was talk of the voice tones (along with the associated guard bands) being used for upstream bandwidth. Obviously this would be miniscule (about 256k, if I remember correctly), but it might serve a purpose for DSL based services from the cabinet for those at a great distance. It all looks very positive from the outset, which is likely why BT haven't bothered to use it.