Not sure exactly on when. But I know I am hearing AT&T engineers are working to get the HD compression down to the level that would allow it to carry 2HD and 2SD. SD is only about 1.5 Mb per stream as where HD is 6Mb per stream. MPEG4
Until ATT can convince copper to defy the laws of physics, they are so screwed, that is the crux of the problem. Copper to the house is NOT a likely solution which is why FIOS uses fiber, which is capable of carrying a much greater bandwidth.
There are other obstacles, but the laws of physics are the ones that are holding them back more than anything else at this point in time. MPEG-4 is very good at compression and decompression, and its not likely to be replaced soon, as I am thinking what you are implying, at least not by ATT. This is NOT the same ATT of old, the one that had Bell Labs (one of my former employers) full of research scientists to get around problems by inventing new technology (think: transistor, fiber optics, etc.)