Nice design, use of cardboard has been tried and tested before. It does offer high energy absorption and better controlled deceleration than EPS, but the properties of it over time are questionable, and from the work I have seen before, the thickness of the outer shell tended to be thicker to provide better support to the cardboard matrix and when taking the thickness of this outer layer into account it decreased the protection due to having lower flexibility.
Maybe not as relevant to cycling but it offers very poor intrusion / penetration protection, so your head would be more prown to injuries from things penetrating through. This is more applicable in aerospace though.