(Based on this Pi-hole as a DHCP / Dual Stack IPv4 & IPv6 and Clients Hostnames + - FritzBox Settings Help)
As of now, we can only set up IPv4 Conditional forwarding, which may not show you the host name on IPv6 addresses, so add an option to let us configure Conditional Forwarding for IPv6 in the web overlay, as manually editing /etc/dnsmasq.d/01-pihole.conf gets dismissed every update.
You can create additional .conf files in the /etc/dnsmasq.d/ folder to pass additional configurations. These files will be read in and applied after a restart, as well they will survive updates.
This is a feature which will arrive with the new web interface and API:
https://github.com/pi-hole/api/pull/178
Is in the pipeline with this PR.
IPv6 conditional forwarding has been implemented in pihole v5.1