Can radicle seeds run over IPV6? Seems like since IPV6 doesn't have NAT it should be a big advantage for p2p and as it becomes more available the need for everyone to set up port forwarding or get a VPS to seed should go down.

ISPs will try to block use of IPV6 for serving content, but eventually I think users will win because ultimately it should be a right to share information.

Yes. Radicle also makes it easy to run behind Tor, see https://radicle.xyz/guides/user#4-embracing-the-onion and there are people that use it via Yggdrasil, see https://yggdrasil-network.github.io/services.html#radicle-no...