2018-05-03 The preferring IPv6 policy is working
Yesterday I changed some IPv4 addresses on virtual machines on the new homeserver to make autofs work. This is a known issue with autofs: autofs does not appear to support IPv6 hostname lookups for NFS mounts - Debian Bug #737679 and for me the easy solution is to do NFS mounts over rfc1918 ipv4 addresses. I prefer autofs over 'fixed' NFS mounts for those filesystems that are nice to be available but aren't needed constantly. It took about 9 hours before arpwatch on the central router noticed the new activity. I guess the policy to try to do everything over IPv6 is working.