Originally posted by Gary
Another possibility might be an automatic expansion valve (AEV) which maintains a constant evaporator pressure, although this may require an accumulator.
Why would someone want a constant evaporator pressure? With constant evaporator pressure, superheat is only OK for one single evaporation tremperature only. For all other evaporation temperatures, superheat is either too low or too high.

Just another crazy idea: why not convert an externally equalised TEV to an electronic expansion valve by putting a constant pressure on the equaliser port, and connecting the bulb to a TEC (Thermo-electric cooler, a.k.a. Peltier element), effectively turning the TEV into a heat motor controlled EEV? By controlling polarity and voltage of the TEC, rapid adjustments of the flow can be made.