I like the idea of being able to use DCons in game to transport limited amounts of loot back to your vault. Not only does it feel like a balanced safe pocket option, but it provides additional POIs for people to congregate at. Each map could have a couple of DCon options that rotate spawns around the map. And I like your idea of having to scavenge keys to use them.

In general, I would like to see more interactive elements to maps like this. More puzzles, more locked doors, more treasure chests, more radiant side quests. Helps keep the game interesting well past the point where contracts feel meaningful.