The more traffic you can get onto ipv6 the less stress is on the v4 infrastructure. Each v6 connection is one your CGNAT doesn't have to provide an ipv4 port for.
You don't have to beef up your v4 infra as much though. Think 4 powerful v4 routers instead of 5 or something. If the traffic to the big streaming providers doesn't have to run through these routers, you can save a lot. Same goes for the ipv4 address space you have to rent/buy. The more connections are on ipv6, the less public ipv4 addresses you need to have.
So ipv6 support might be saving you costs already in a dual stack setting.
Take a step back to the wider context of a brand new ISP though. If you’re rushing to market like Starlink appears to be, you either implement just v4 and scale later or implement both v4/v6 up front.
Until there is a bunch of exclusive v6 stuff customers will be up in arms over missing, the answer of which thing to prioritize is obvious.
Yeah I guess it's the same as with the inter satellite communication which is promised for later, but not implemented yet so that they get at least some product out to customers. I don't think dual stack is that hard to do for entirely new networks though.
Also, one of the reasons to do satellite internet is lower latency which is a bit hurt by CGNAT infrastructure.
Last, generally brand new ISPs are in the situation that they have a hard time of getting ipv4 address space. The incumbents, especially the older ones, were around when ipv4 addesses were still plenty so they usually have way less problems with ipv4 address space. Starlink only has 166k ipv4 addresses according to https://ipinfo.io/AS14593 . Compare this to AT&T which has over a hundred million for their AS 7018 https://ipinfo.io/AS7018 alone, and there are other AS numbers they have like AS20057 with 7 million ipv4s. This roughly matches the number of AT&T customers while Starlink has more than double the number of subscribers than its number of public IPs, with growth ahead.
