is that something that is going to be added?
so far I have found a sort of a solution[https://askubuntu.com/questions/990195/ipv6-tunnel-in-ubuntu-17-10 (https://askubuntu.com/questions/990195/ipv6-tunnel-in-ubuntu-17-10)], but it is still an issue to get it rolling, as it seems to me.
Netplan is horrible for tunneling (Ubuntu should've never ditched ifupdown in favor of that). I tried the configuration that you linked to and ended up breaking a completely fresh Ubuntu installation to the point that it completely stopped responding to DHCPv4 requests (yes, even something completely unrelated to IPv6 tunneling causes it to break, and I'm 100% sure that that YAML structure in the configration file is correct), forcing me to do yet another fresh install.
You're better off stuffing the Linux-route2 example configuration in a systemd unit (https://blog.donbowman.ca/2018/03/15/i-yamld-my-network-netplan-and-the-new-world-order/), that's how I've done it now with a whole lot less fuss and drama.