Most ultra high efficiency heat pumps are already using DC inverter technology which allows the compressor, fans and pumps to run on fully variable speed. If Electric Air is planning on using DC components for their heat pumps, they could make it DC powered as well. The issue is that it would increase cost substantially for people who don't necessarily need it since a 5KW class DC controller (to run the aforementioned off of solar) would add a good chunk to the bill of materials. It would also add a lot of complexity to the system. Lastly, it is only really practical in hotter summer climates for cooling where your cooling demand and sunshine line up nicely. In heating applications, you need the most power when it is cold out (in the middle of the night) and so the demand and generation is almost fully inverted.
One feature that would be great (and universally practical) is using the heat pump to heat water with the waste heat from air conditioning in the summer (or when any time the house doesn't need the air heated). Add to this the fact that heat-pump water heaters are in the $2000 range, and eligible for many credits - it could be a great add-on.