Possible to add heat pump to the REx?

[Surge]

In another post I tried to calculate the efficiency loss of the REx vs. the BEV, and with the help of some forum members, it works out to somewhere between 10-17%. About 7% of that is due to the heat pump in the BEV. We know that the heat pump heats the cabin 30% more efficiently than the heater in the REx. (Although we don't know if the 30% applies to specific outdoor temperatures.)

But what if you could install the heat pump in the REx?! It may not be impossible.
We know from BMWi3Owner's post that the heat pump is in the front:
http://bmwi3owner.com/2014/02/heat-pump-in-front/

Also, look at this pictures
With heat pump:
http://realoem.com/bmw/showparts.do?model=1Z22&mospid=56088&btnr=64_1955&hg=64&fg=18&lang=en

Without heat pump:
http://realoem.com/bmw/showparts.do?model=1Z22&mospid=56088&btnr=64_1956&hg=64&fg=18&lang=en

You'll see that the heat pump is just an add on that takes coolant and runs it through the heat pump. Look at hoses 4 and 5.
Also look at the vertical slender object "flow heater elec" in the diagram below:

http://realoem.com/bmw/showparts.do?model=1Z22&mospid=56088&btnr=64_1957&hg=64&fg=18&lang=en

Seems like if you have the heat pump, the coolant runs through it, otherwise hose 4 just runs from the flow heater elec right into the electric water pump (9).

One question is - are all the electric water pumps the same? They would need the extra fitting for the heat pump. They appear to be the same, but maybe someone with a REx can take a picture of it?

 

[Surge]

Alas, there is also a pipe going from front to rear that the heat pump cars have.
So it doesn't seem possible

 

[I33t]

If the heat pump is water sourced rather than air sourced, the efficiency may be higher than I thought previously, and it would hold out better in low outside temperatures.

My theory as to why the Rex has no heatpump:

Assuming that it is water sourced, and using the same coolant that passes through the battery pack, I think you have your answer: When the Rex motor is running, the battery pack is not generating heat - the heatpump will suck heat out of the battery pack coolant and battery. Probably, there is a potential for the heatpump to freeze the coolant (and battery pack). Plug that into -10C temps and you will quite possibly have a battery and cabin heating catastrophe.