My use case is, that my ISP is lacking IPv6 support. Since I have started to use IPv6 only services, I plan to route all public facing IPv6 traffic through an Ipv6 egress gateway on a linode (=netmaker central host). A second family site has an egress gateway for the offsite backup location.

this should be fine, just make sure not to use the netmaker server as the ipv6 gateway; we've disabled that (docker-compose does not play nice with ipv6)