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New refrigerants will make a big difference here. The main theoretical restriction is the pressure delta required to go from a low enough pressure to transfer heat into the system at a low ambient temperature, then to a high enough pressure to transfer heat out of the system at a high ambient temperature. That’s what causes the loss in COP at low temperatures—the increased work the compressor has to do.

It’s definitely theoretically possible. There are refrigerants that can do this now with a relatively low delta, but generally they are flammable, toxic, or have high global warming potential.

There are other ways around this like booster systems, but it becomes a $$$ issue at that point.