Similarly, I've heard that the cockpit voice recording only keeps the last two hours. While that deals with 99% of the cases, here it will miss out on all conve

Similarly, I've heard that the cockpit voice recording only keeps the last two hours. While that deals with 99% of the cases, here it will miss out on all conversation near the point that the flight began to go off course, and indeed hours after that. What would be the cost to simply bump the recording time up closer to the maximum flight time possible on a full tank?