Posting this here for more visibility, got buried pretty quickly with RME talk in Discussion. Ligray linked us to a JP site interview done with 4 people from the dev team:
http://www.4gamer.net/games/005/G000546/20130501051
There was some interesting (but late) info on Skirmish segments. Basically, it sounds like there is always a constant number of Skirmish items around. Each one is flagged for a particular area and action (e.g. Logging in Ceizak). Until that piece is obtained, it will not move elsewhere. This explains why it's easy to obtain pieces quickly sometimes and it takes forever other times (you're waiting on someone to obtain one somewhere else to get it to spawn for you). So if you're farming Skirmish stuff it makes sense to just do as many different things as possible for short times each.