Not sure about US, but Indian ISPs are doing this already to conserve IP space given huge userbase. In theory it would work similar to how a NAT gateway works for outbound communication. Skan + geo would be hard nut to crack in India.

Some USA ISPs do CGNAT, some don't. I'm not surprised to hear either way here.

In UK I'm now on FTTP but even on ADSL the house would have an IP address that normally stayed constant until a router reboot. This seems to be pretty common in the UK. Probably on cable internet (and on mobile ofc) you get NAT-ed but I've never had that.

In Australia most ISPs use CGNAT by default and you have to specifically request a dedicated IP if you want to host a Minecraft server or something.