That actually would work for some others in the US also, except it goes against the one ARC Dish wants. But in theory if you could put all HD on 72 that is not on 119/110, and put the remaining HD on 61.5 that helps PR, but also those that have trouble seeing 129. You could have 119/110 and 61.5 if you needed to. Unless I'm missing something, again in theory that would work.
But it does bring up a couple of problems. As mentioned, that would be promoting mixed ARC use, so dish would have to be ok with that to actually make the changes specifically to allow that kind of use. And it still may somewhat make adding channels harder as that is one more thing to worry about when you need to move a channel especially on the WA Arc. It would make moving a channel off 119/110 to 129 cumbersome.
Second, that is mixing Mpeg2 and Mpeg4 Sats. Fine if you have an Mpeg4 receiver, not fine if you don't.
If Dish does not want to deviate from the two ARC system, and they do not see a connection between 119/110 and 61.5, then I don't see them officially doing this. But will it work? Yes I think it would.