Just because you'll have enough ipv6 addresses for every website doesn't mean you'll want to actually do that.
It's a lot of extra hassle to set up dozens of IPv6 addresses when (e)sni can do the same job.
Moreover, (e)sni has an advantage over using ip mapping; events if someone is snooping on your connection and can see that you are connecting to some ip address they won't be able to determine what site that might be.
If you are simply mapping IPs, they can visit that to see what you are visiting.
It's a lot of extra hassle to set up dozens of IPv6 addresses when (e)sni can do the same job.
Moreover, (e)sni has an advantage over using ip mapping; events if someone is snooping on your connection and can see that you are connecting to some ip address they won't be able to determine what site that might be.
If you are simply mapping IPs, they can visit that to see what you are visiting.