If only there was some technology that would allow every peer to have its globally unique address, making direct connections only a matter of firewalls.

I don't know, something like IPv4, but with more addresses...

Both tailscale (partially open source) and nebula (entirely open source, you have to host the "lighthouses" which assist in NAT punching yourself) do this. (Also tinc.)

Yggdrasil is basically researching a replacement for BGP, so hole punching isn't a priority. (There is a 3rd party project that does something like this for Yggdrasil, but nebula is probably the better fully open source option.)

On ygg as long as the nodes are reachable they can peer. If your nodes are on LAN just turn on multicast peering it's fire and forget.