One usecase I've always wanted is being able to combine multiple tunnels into one shared connection, for instance airVPN allows 5 simultaneous users per sub, it would be awesome if I could run 5x connections and combine their traffic, but I dunno how I would do this with wg / nmcli
VPNs are level 3 while interface bonding is level 2. You’d have to create a vxlan over wireguard. It sounds like a nightmare but it would be interesting to implement.
I’m just gonna leave this here: https://docs.zerotier.com/protocol/#bridging
Disclosure: I work at ZeroTier :)