For countries, if you meaning connecting to VPS, lot of countries have good IPv6 connectivity now.
For me both ISPs I use have native v6. This will differ from person to person.
It is inconcievably stupid that github, run by a massive tech company like Microsoft, has not migrated to ipv6. They're single-handedly holding back adoption.
There may indeed be some tracking that MS does via IPv4, but it's not a good way to do it.
I suspect any such tracking is essentially just some cruft that snuck in (either their own or legislative) in the early 2000s, and nobody thinks it's their problem to make go away.
That said, that IPv4 is a poor way to do tracking doesn't guarantee there's no manager demanding it: any corporation eventually gets someone with no technical knowledge demanding bad solutions.
Responsibility and controls. If the host/dc assigns a dedicated addresses the contract can be essentially "the customer assumes all liability behind traffic". With NAT/LB you need at the very least quite robust, evidence-grade monitoring mechanisms tagging all traffic and keeping historical data. In practice, some for of active abuse prevention is required, otherwise huge chunk of your address space is going to effectively linger in blacklist limbo.
That is, if being unreachable below "presentation layer" is acceptable in the first place, but I guess the question kind of presupposes this.
