I don't think we want to have 'magic' registry entries that are computed dynamically, at least not inside the normal branches. There are dynamic branches like HKEY_DYN_DATA where we will need that, but I think the rest should use the normal update mechanisms. For things like plugging in a new interface, there should already be callback scripts in Linux that you can hook into to set the corresponding registry key.
So that leaves either initialising these entries at wine install time (which is what windows does it seems, i was wrong about it computed at startup), or at wine startup.
Install time is an extra step that would increase packaging complexity. Wine startup would hit startup time. Perhaps, check if the keys exist at startup and if they don't, create them? If the network config changes perhaps a small winelib app that recalculates the keys could be used - tying into kernel notifications could come later. Would that be OK?