How to combat Double NAT issues as a carrier?

For some time I have been trying to look into how a carrier can combat issues regarding Double NAT. The issue I see is with carriers starting up CGN without really helping subscribers (or in some cases even informing them). Most articles online are for the subscriber and what they can do, but what can the carrier do to help them?
So far this is what I have found as a way around Double NAT:
Buying a VPS and funneling traffic through a VPN
Selling public IP addresses Allowing subscribers to take multiple IPs and allow port forwarding Sell Public IPs
This seems terribly restrictive and difficult to implement. Are these really the only options available? Most of these also require the subscriber to buy a service or rely on their ISP to not switch to CGN. Does anyone of any ideas what can be done either to help a carrier help its subscribers.