The idea is based off of Sam and Frodo’s use of orc armour to ‘blend in’ in Mordor and I believe that a similar idea would allow for an alternative (and optional) gameplay and mini-quest style.
The concept is rather simple, when a player is wearing the complete set of armour from an enemy faction, the said enemy faction (and only that faction) would be unable to detect the player until the player was within 8 blocks(?) of the npc rather than the usual 16 blocks. As an example, say I am a good aligned player and I enter Mordor wearing a complete set of armour from any of the various Mordor sets. The Mordor faction would not notice or attack me until I was within a certain distance of them.
The twist to this mechanic is that the armour would only work on their origin faction. Again as an example, Mordor orc armour would help the player ‘blend in’ only in Mordor but not in Dol Guldur. In order to ‘blend in‘ Dol Guldur the player would need Dul Guldur armour.
This mechanic would have the benefit of making every armour piece in the game useful as one could then use each set to infiltrate certain factions (and subfactions). Another benefit of this mechanic is new mini-quests. As an example an npc could ask the player to infiltrate an enemy orc camp located at x y z and retrieve object A without being detected.
This idea is not set in stone and is mainly my desire for stealth gameplay in the mod.