As best as I can determine from bean counting I have done previously, DirecTV fully utilizes the available uplink spectrum at its three Ku locations, and therefore no channels can be added on a regular basis without deleting some. Adding an MPEG2 HDTV channel would require dropping about six or seven standard definition channels
DirecTV 4S and 7S have backup transponders onboard that can be matrixed in to replace malfunctioning units. There are also a couple of older satellites whose names I no longer remember that are "stored" conveniently such that they can provide backup conus beams, which could in turn free up additional agile transponders on the spot beam satellites. You may recall the trouble that a lot of people had with HBO on transponder 30 a couple of years ago. The informed speculation was that they were temporarily broadcasting it off a single powered (120Watt) transponder on one of the older satellites and it was getting beaten up by the higher intermodulation floor that results from now having double-powered transponders for the other CONUS beams, as well as the high intensity spot beams. In Los Angeles, for example, transponder 28 was about 11 dB stronger than transponder 30 was when it was weak, and some devices, like the Sonora SAL 20-24 stacker, with its automatic gain control (AGC), basically forced its amplifier to beat up the weaker signals. I actually bailed out one MDU by changing from an SAL 20-24 to a cheaper, residential Sonora 575 microstacker because I could pad down the stacker input without getting thwarted by an AGC. But even if DirecTV used one of its backups satellites to supply a CONUS beam or two, thereby freeing up 4S or 7S hardware, there is just not any uplink space to accommodate that programming, unless 7S has the physical capability to receive uplinking from a fourth site, a capability of which I am not aware.
At some point, DirecTV will determine that enough MPEG4 receivers have been installed or are available to be installed to meet the needs of customers who only want them for additional HDTV programming. My own wild guess is that could be a year away. In the mean time, I can't tell any customer in good conscience that DirecTV provides the best answer to fulfil their HDTV needs.