Here's another crazy idea.
It would interesting if a variable refrigerant volume system, like Daikin, could be married to a direct exchange geothermal unit like Earthlinked.
Because the refrigerant phase changes in the ground during the heating mode, a DX system is much more efficient at extracting heat from the ground compared to a water sourced system. And the Daikin system avoids the heat loss typically experienced with ducts in unconditioned spaces where they are normally found. In addition, Daikin systems are smart in that they can channel the refrigerant wherever it is needed and avoid where it is not needed which contributes more to it's efficiency.
The issue with this idea is the Earthlinked system has to maintain a certain velocity of refrigerant in order to keep the oil, that is entrained in the refrigerant, from "pooling" at the bottom of the earth loops. Daikin's system can have refrigerant runs as long as 1,000 feet which would cause compressor failure if the two refrigerant circuits were connected.
I'm wondering, however, if the two refrigerant circuits could be kept separate and still work? I am picturing a copper-to-copper helical coil design, similar to the Earthlinked desuperheater, where the heat is efficiently transferred from the Earthlinked circuit to the Daikin circuit.