Aside from comparing assigned public IP addresses regularly, I think we (ipinfo) probably have this data internally, or at least we can figure it out. We are pinging and running traceroutes on every IP out there to figure out IP geolocation, so I think we should be able to tag ASNs/ISPs that use CGNAT. So, on CGNAT connections the RTT on the same IP address will be different from time to time and traceroute paths and times will be different as well.

But I'm not sure who will and how they will find this information useful. If anyone can think of a reason why CGNAT detection can be useful generally, I can pitch this to the engineers.