Do we have any reason to think D12 is better suited in some fashion for the hypothetical new encoders? If not, this looks more ominous than happy-making to me. . . like a risk management thing.
The reality of the situation is that we just don't know, and there are many possibilities.
It's quite possible that certain channels may be a better fit to be combined with the new encoders and this was one of maybe many steps to re-arrange things.
They didn't just move every channel from one transponder to another. When you study line-for-line what they did, it appears that they carefully moved channels around to different spots.
Also, maybe it was easier to start with D12, especially D12 transponders 9 & 10 because they weren't being used before. Maybe you first light up two new transponders with new encoders, and then slowly start moving stuff week-by-week, every Wednesday.
Personally I'm excited to see the activity. It's crystal clear evidence of a move to 6 channels per transponders.
Now we just need to see how this plays out.