I would even be happy with being able to set the IP address simply as a form of documentation.
It seems wrong to have to open the HMI config to find out what the PLC's IP address is.
Host isn't the only one that is missing this info while offline.
I think the issue here is that a PLC's Ethernet port can be used as server and/or a client. Depending on what you are using the port for greatly affects where it should be set and the significance of the IP address (or lack of). What is the IP address of your PC? Who cares. But what is the IP address of a critical server? I don't know the IP, but I do know the name that gets resolved to it.
Our introduction to automation hardware was the ECOM. Where is the offline config for it? There isn't one. Since ECOMs can be server or client, DHCP and static IP may make sense or not, but the config is always online. Since we had no hope of getting help from the PLC to configure the ECOM, we built NetEdit, and that became our focus for all Ethernet setup everywhere.
When we built out first PLC, it honestly never crossed our mind to put the IP address in the system config, since nearly every PLC at Host uses the Ethernet port as the programming port. When we first started hearing this request, we scratched our head...we had no idea why you would want it. I'm still a little fuzzy on it, but I guess when you are using the PLC's port strictly as a client, it would make sense to add the config to the system config. And we will.