I've been pondering this question for a while and I think I must be missing something. In a regular refrigeration cycle you have a high pressure liquid at nearly ambient temperature entering a metering device and then an evaporator coil. At which time it is a low pressure and low temperature gas. This gas exits the evaporator while still fairly cold. Why not put a regenerative heat exchanger to cool the liquid as it's entering and heat the gas as it's leaving? The gas is just going to the compressor anyway and the compressor doesn't care what it's inlet temperature is. The resulting high temperature gas from the compressor outlet would be hotter, but this would allow better heat transfer to the ambient air in the condenser. Seems like a surefire way to increase efficiency to me, but I don't see any real world applications. What am I missing?