Thanks a lot for your answers!
I agree with Dave that probably most nodes that offer an IPv6 endpoint are dual-stacked.
Is this just something you'd like to know "for fun" or are you curious about how decentralised cryptocurrency is.
I'm working with IPv6-only machines and I'm wondering if there could be a security risk when connecting only to the advertised IPv6 addresses.
For example, if the number of IPv6 nodes is small and these node are separate machines, an attacker might try to get them all to extend a fork. However, if these machines are part of the IPv4 network as well, this risk is reduced because the nodes still obtain the proper blocks.
Does anybody see security risks when running IPv6-only machines?