I think they couldn't modify the sub to be safe - the big worry is the integral part of the sub (and the one with the highest cost in this one), the composite p

I think they couldn't modify the sub to be safe - the big worry is the integral part of the sub (and the one with the highest cost in this one), the composite pressure hull. You cannot ensure its safety, since you cannot evaluate it for growing defects. As is best practice for all other DSVs in the world that use metal pressure hulls. I suspect a metal hull and all it entails (way more complex design and careful selection of materials, equipment, passenger space etc.) would have cost too much.