Killing off MPEG2 HD was easy, because it was around for such a short time before MPEG4 HD came out, so there weren't many subscribers. More importantly, those subscribers were were all early adopters, who would be much easier to migrate than the laggards subscribing to SD only in late 2013.
I think understand what you're saying now, you would introduce MPEG4 versions of channels that are only available in SD. Those available in HD wouldn't get a MPEG4 version. I'm not sure so about that. Watching a 16:9 signal letterboxed or vertically stretched on a 4:3 TV is just as objectionable as watching a 4:3 signal on a 16:9 set with the same compromises in the other direction. They'd risk losing subscribers to other providers who provide proper 4:3 versions of the channels. As more providers offer only an HD signal (I think ESPN is already there?) this won't matter, but until then it will.
It seems you're suggesting that providing a MPEG4 version of a SD only channel should be done in advance of dropping the MPEG2 version. If so, I fail to see the point. All MPEG4 receivers can receive MPEG2, so as you upgrade people to MPEG4 capable equipment they can still watch the MPEG2 version. Only when you switch off the MPEG2 channel would you turn on the MPEG4 channel. What's the point of doing it earlier, except to waste bandwidth?
You say "You can't have everyone change out all their equipment in one day and flip sd stations from moeg2 to mpeg4 also that same day." That's a red herring, because you don't need to change out equipment in one day. Unless you are suggesting Directv should build equipment that cannot decode MPEG2 at all, which makes no sense, you can take years to switch out all the equipment in an area, then flip the switch on their locals in one day. When it has been done everywhere, the switch can be flipped for all the remaining MPEG2 SD only channels in one day.
Given how far Directv is from doing this, by the time they think about dumping MPEG2, the migration may happen not to MPEG4, but to HEVC