The reason why I ask is for different builds.
One of the main reasons i don't play much PvP is because i hate having to manually reorganize all of my abilities and make room for the exclusively PvP skills and abilities.
It occured to me a while ago that if a player had the option to attach skill slot layout to their gear set, rather than the entire job, they could more easilly manage this.
For example, Having a Gear set named "MNK" and one named "MNK PvE". If this were a reality, a player would not only be able to assign gear to the different sets but also have all their Pve Skills in a certain order for "MNK" and have their PvP Skills in another order for "MNK PvP".
This would require some elbow grease to work out in the back end of the system, but i think it would be an amazing advancement.
I know i'm not the only one who doesn't do PvP mostly for this reason, either.