I am not asking to castrate WG in any way and suppose you are referring 
likely to WG clients when citing a roaming scenario, at least my servers 
are not roaming.

And on a server I prefer tight control over what is happening with the 
network. Hence, it would be good to have an option (enhancing WG) in the 
settings/configuration:

- choose ip protocol version - ipv4 or or ipv6 or both
- bind WG to either iface(s) or subnet(s)

I trust that such is available and common practice with other VPN apps.

> If wg was binding to a particular interface, I don't think it would be 
> possible to support roaming scenarios. I have a travel wifi router, 
> and I love the fact that it will automatically switch between 
> connecting through the Ethernet interface or the USB tethering one.
>
> The need you describe is orthogonal to the role of wireguard. If you 
> want to tightly control what wireguard is doing, you should use 1) 
> good routing rules and 2) iptables to match these rules.
>