3-terminal adjustable voltage regulator: elegant way for Vout=0 when Vin<(setpoint + dropout)?
Any more elegant solutions out there?


Sure there are. Just look for a regulator with a pin called UVLO. It stands for under voltage lock out and has internally a comparator that switches off the regulator's pass transistor when the input voltage is too low as set by a resistive potential divider applied externally to that pin.