My main concern with IPv6 has to do with privacy. With IPv4, most of the internal networks aren’t visible outside the firewall but with IPv6, every single device is more likely to have its own address which could end up being directly visible from the internet.

Although device-specific firewalling might emerge, I feel IPv6 could make it more difficult to maintain true privacy. IPv4, with its inevitable internal addressing, seems more effective at preserving privacy “by default”.