Black Market Connections (BMC).
Steal is not useful or fun anymore, so replace it with something similarly shady, but useful.
Simple version: when bartering some types of items, you get a discount or sale price bonus.
Stack BMC with Barter or add it to Reputation, or both.
This would apply to drugs, lockpicks, explosives/mines, detonator parts (if in a store- dialog purchase would require more work to implement), and special items like HQ EP, Polymers, HQ fibers, access keys/cards, oil cans, and possibly some high end gear. Again, this would just be for bartering in shops, as modding dialogs would be too tedious.
More complicated version: Thieves Circle, Gunrunners, Slavers, Mordinos, others have an informal network with quests/etc. Other groups may want to infiltrate them, etc.
Not sure if Black Market should be a faction, or what do with their faction points.
Maybe even make those FP the only way to increase BMC (players with Steal already would get a 1-time map-over of points).
Possibly allow bartering of the affected item types increase BMC, similar to Scavenging.
Or do something else.
Maybe BMC FP would just allow buying special items (dialog items?) from the "Contacts".
What to do about the Thief Perks?
Make these just give more discounts for BMC stuff?
(Flat 5%, 10%, 15% Thief/pickpocket/master thief, either +5 each, or cumulative +5+10+15)
Then what about Harmless Perk?
Double the "parley"?
That is, NPCs in encounters take twice as long to react. (plus one second?)
Also positive reputation would decay at half the speed, and negative at twice the speed.
"Aw, that one is just so harmless!"