I really like this exercise to help increase hip mobility while really blasting the legs. The Bulgarian split squat by itself is tough enough but by performing this exercise from a deficit you can get additional benefits. Look closely at the range of motion the hip can go through to complete the movement when your squat leg is on a step.
One way you can progress this exercise is to use dumbbells in each hand, which would requite additional muscle activation and stabilization. However, a unique way to progress this exercise is to add a light dumbbell to the support leg side. What this does is it encourages your hip external rotators and abductors to work harder eccentrically while the hip flexes to counterbalance the internal rotation and adduction that the hip want to go into due to that weight.