In principle, IPv6 core networks can actually be very beneficial for small providers just starting out if they're not able to get IPv4 addresses for their customers and are forced to use CGNAT.

In an IPv4-only CGNAT setup, all the traffic has to flow through the CGNAT gateways, and that gear is stupidly expensive. Having IPv6 in the mix means that anything that supports IPv6 (such as most streaming services) won't hit the CGNAT gateway and can just be routed natively. This can really save money on CGNAT hardware.

For implementation, you can use NAT64/DNS64 for your CGNAT setup and implement 464XLAT on the CPE. This keeps your whole edge network IPv6-only so you don't have the complication of maintaining two parallel configurations on the edge.

There is also MAP-T, which is even lighter on infrastructure since it pushes all the state into the CPE and avoids the complication of stateful CGNAT. But unfortunately CPE support for it is pretty limited at the moment.