For the record, Dmitri did some initial reserarch on this but the effort ceased AFAIK.
Dmitri no longer works on Foreman full-time. I wonder about the future of the IPv6 implementation in the netboot package: Commits · danderson/netboot · GitHub and for this reason I would suggest to focus on integrating with Kea or dnsmasq. The major concern for Satellite team is supportability by Red Hat - currently only dnsmasq is in the base RHEL repository (thus getting full support), Kea is only in EPEL (no official support).
Of course anybody from the community is more than welcome to start working on Kea DHCP module for smart-proxy right away.