I think as a general rule, if an area is blocked off by a traffic cone or a construction sign, it means it's a WIP and will be added eventually. Don't expect it to be too soon though, some areas have been blocked off for quite some time without updates - the Urotsuki head in Flesh Paths World and the dark path in the Flooded City are 2 of the older Coned off areas that come to mind - I'll have a look at the map in RPGmaker and see what's down there (if anything)