These days I would expect to reach for wiregard for p2p vpn solutions. Are there any advantages to using IPsec instead? Is this for connecting to some existing IPsec infrastructure?
Also, as this tunnel interface still integrates with OpenBSD isakmpd (IKEv1) and iked (IKEv2) daemons, you can use certificate-based authentication without installing some bespoke, proprietary agent for key management.
> The reason I started on this was to better interoperate with "site-to-site" vpns, in particular AWS Site-to-Site VPNs, and the Auto-Discovery VPN (ADVPN) stuff on fortinet fortigate appliances. Both of these negotiate IPsec tunnels that can carry any traffic at the IPsec level, but use BGP and routes to direct traffic into those tunnels.