An approach that is unstable below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around.
Would it be worth considering a 'Mode 8' for EGPWS? Something along the lines of speed VREF to VREF + n, V/S between 500 fpm 1000 fpm at 500 feet otherwise "UNSTABLE GO-AROUND". Like an RA this would be a mandatory instruction.
I wonder how many unstable approaches actually occur each year that do not result in an accident, but are close.