The reasoning is as follows:
They are equipped on your person, just not in your hand. They function in a similar manner then to that of armor at that point, being static on your body.
For shields, it's as if you had a shield on your back. you would gain the defensive bonus, and the set bonus (if any).
For weapons, it's as if you had them sheathed at your side. you would get the set bonus (if any).
For sets that augment abilities (like the maelstrom sets, asylum sets), the built in constraint would be that you need to use the weapon type in order to use that bonus if the maelstrom/asylum weapon set bonus is acquired from your off-bar. This could be further expanded upon by stating and requiring that the weapon must be held in hand to gain that set effect.
The maximum number of slots then would be 14, not enough for 3 5-piece sets, but would certainly allow for some wonky interactions with the weapon sets (3-piece sets) used with sword/shield and DW builds.
Edited by Avran_Sylt on October 17, 2017 3:08PM
Should Off-bar Weapons/Shields count towards your Set Bonuses/Armor? 9 votes
Maybe, but would need theory-crafting on potential edge-cases.
No, it would throw a wrench into too many things.