The problem with adding this as a migration target is that we would need to remove others, as the SE team strictly limits the number of targets and (without having hard numbers at hand) I don't believe that we get more networking questions then those that would be migrated to one of the present selections (SO, SU, DBA, U&L).
If you see a good(!) network engineering question, just flag for migration.
Adding it to the help page is a good idea though, as the only reason it wasn't added earlier was likely that it was still in Beta at the time. I'll have to check if mods can edit this text or if we have to take this to a community managerand I've just done so.