Sport canopies have used reefing systems for years. The faster you're going, the stronger the resistance to the canopy spreading, with the reefng force directly proportional, so the part-open canopy slows you until a speed when the spreading force overcomes the reefing. (If a modern, aerodynamic 'square' canopy opened without any reefing it would generate instant drag and lift, which would not be good for it or you.) I guess that a reefing system is impractical because of the need to cater for for a very low ejection, though.