My 3 ton water to water unit actually keeps the house warm all winter, with the occasional fire in the woodstove. But my hot water is all electric. (no nat gas here). A desuperheater will provide some hot water during days the heating (or rarely cooing) runs, but it would add to the load of the 3 ton heat pump.

So I go looking for a standalone domestic hot water tank that uses a heat pump. There are none?!. There are some that have a small air based heat pump on top, which works well for the southern states, but nothing for up north here, where there is heat in the ground.

Then I found ONE in Europe. They look expensive, and there are no dealers here. The Heliotherm H300BE-WT PDF

What would be the closest thing to a standalone domestic system? My take would be two electric HW tanks, one connected to a small heat pump, the other as a finishing tank. The first would heat the buffer tank to say 110 - 120F, then the electric tank would be set at 130F or so. Then the recycle time of the Geo tank can be hours - the electric will take the extra load. I can't even find a 1 - 1.5 ton water to water unit to make this work?

Is there something that I am missing - or is this an opportunity? The price of electricity is going up fast.

All of the stand alone geo domestic water systems we have done have all come out eventually. Space required for storage was to great, maintanance issues were a pain, the popularity of tankless with lp or natural gas has sky rocketed.
My best scenario concept allways involved desupraheater or water to water to a buffer tank and then to the tankless for finishing. The advantage to adding more equipment to a system that is allready efficient gave me pause from execution of the plan.

If you have already a 3 ton W-W unit you can run the hot water tank as a zone thru a heat exchanger. You loose some degrees (5-7F) but 118 Degree water is still pretty hot. Works like a charm to me. Full time domestic hot water. It will steal more heat from your heatpump, if you set it to prioritize on the DHW.

A truly standalone water to water geothermal domestic water heater exists - WaterFurnace model EW020. It has a double wall and vented heat exchanger suitable for domestic hot water. However, it needs to be plumbed to a storage tank.

I might do that. It may require quite a bit of plumbing, though. Thanks.