In real life, there are places you cant get in without suit or tailcoat.
In post apo world, there could be a place or places, where you can go only in special suit. So i suggest:
+
Make robe as a item you need to wear on, if you want to enter Cathedral or other places where Hubologist or other church are. This will mean, that
without this item,
they will kiill you, because they will think that you are not one of them and
with robe, you will be
able to trade with NPCs there, or at least, you will
be in safe in every place where is this kind of church. Safe against PK without wearing a robe, of course
* Also, you have to make "rare item", so dont enable crafting of this robe.
* Add hubologist into the all churches in the cities
Am i genius?
P.S.: Robe could be red, not dark, does not matter
Explanation why robes: I will rather see that you can join Hubologst or other church and you could benefit from this your faith (acces to the NPCs, small protecion in few houses in wasteland). Your faith will exclude you from other church or your karma will drop in some cities, but can you realize, how long we have to wait for another quest? Half of a year. This change could be implemented very fast, dont forget it.
Your desert robes could exist simultaneously to red robe, that will qualify yourself to trade with that NPC and protect you at those places. Consider it as a first stage of religion/fate element in the game. Dont forget that this is FALLOUTSISH more than Jet!