The current min version for dnsmasq is 2.59 but when testing out ipv6 with this I found that 2.59 doesn't support tags on ipv6. Bumping to 2.63 solves the issue.
$ sudo ip netns exec qdhcp-0daab4ab-609d-4736-ba91-a85efc755ab6 dnsmasq --no-hosts --no-resolv --strict-order --bind-interfaces --interface=ns-4d62b93a-7d --except-interface=lo --pid-file=/opt/stack/data/neutron/dhcp/0daab4ab-609d-4736-ba91-a85efc755ab6/pid --dhcp-hostsfile=/opt/stack/data/neutron/dhcp/0daab4ab-609d-4736-ba91-a85efc755ab6/host --dhcp-optsfile=/opt/stack/data/neutron/dhcp/0daab4ab-609d-4736-ba91-a85efc755ab6/opts --leasefile-ro --dhcp-range=::,static,86400s --dhcp-lease-max=16777216 --conf-file= --domain=openstacklocal
dnsmasq: bad command line options: only one tag allowed
Removing RC1 milestone for havana-rc-potential bugs: those are nice to have, not release blockers.