Achieving a pistol squat isn't enough an end-goal, similar to what Coach Sommer says about muscle-ups - if completing a muscle up is the sole target, athletes aren't prepared for more advanced variations.
Pistol squats is now too easy, holding 10 minutes unassisted bodyweight. But how to create further challenge to express even greater dorsi flexion?. what is terminal dorsi flexion? can the foot touch the tibia?, perhaps a contortionist could.
Animals literally rest their tibias on their feet when they sit so it's definitely an advantageous biomechanical position for horizontal force production economy, perhaps Humans could do this too. I know people in Africa can run up trees with amazing ease, perhaps they get awfully close to terminal dorsi flexion.
If a basic pistol squat unassisted is level one ,then how does the athlete progress from there to harder variations?
I feel ultimately the pistol squat archetype suffers from lack of 'ROM' progressions in gymnastics because it's not necessary for competition thus ankle ROM protocols haven't been fleshed out anywhere near the sophistication of shoulder joint work.