In resource challenged regions we have been using IPv4+CGN+IPv6 dual stack for the last ten or so years. For 20K subs you can use one /24 of ipv4 and a /40 or so of ipv6. There have been available RGW’s and sufficient vendor support throughout this time. The only issues I have ever really seen have been with Sony PSN doing random ipv4 /32 blocks. Apart from that it has been working just fine. Over 50% of traffic now flows on the V6 side and in general end customers have no clue, it just works.

>For all I care we already have a perfect working system with IPv4+CGN+IPv6. The CGN part was the most troublesome, not the IPv6.