CGNAT scaling cost (was Re: V6 still not supported)

An oft-cited driver of IPv6 adoption is the cost of scaling CGNAT or equivalent infrastructure for IPv4. Those of you facing costs for scaling CGNAT, are your per unit costs rising or declining faster or slower than your IPv4 traffic growth? I ask because I realize I am not fit to evaluate the issue on a general level, as, most probably due to our insignificant scale, our CGNAT marginal costs are zero. This is mainly because our CGNAT solution is oversized to our needs. Even though scaling up our currently oversized system further would lower per unit costs, I understand this may not be the case outside our bubble. - Jared