Even for a couple of servers that do not have an external firewall filtering packets for my IPv6, there is basically zero packets besides those going to applications hosted on my servers, and they have published DNS records for web and DNS. Some basic PCs I have online see zero packets from random internet hosts on IPv6.
The IPv6 address space is literally too large to crawl within any useful amount of time. If you figure an average LAN will have 18,446,744,073,709,551,616 addresses (a /64 block). Let's say you scanned 1000 IP addresses per second (very optimistic for a single PC) it would take you 584,942,417 years to complete scanning just a single LAN. Then are so many /64 LAN blocks that it is very likely you're scanning an network block that does not have any hosts to begin with.
There will have to be other means to gather active/in-use IP address such as looking at server logs that clients connect to, email headers, DNS records, soliciting traffic from the client machines via some application/trojan/virus, network traffic sniffing, etc. All of these means already exist for IPv4 so there is nothing new there.