I would like to see locks implemented at some point, where a locksmith can create a standard lock and a master key. The locksmith can then use a forge or something to create as many copy of the key he want. The lock can be added to any coffer, door gates, etc... by selecting it and right clicking on the object. Once locked, anyone that own the right key in his inventory can open the container/door.
There would of course be a second skill, picklocking, to open lock without keys. This skill should take a while to use, and it should be visible to anyone within sight that a lock is being picked.
There might be issues if someone lock a player inside a house and the victim does not have the lockpicking skill. Doors should always be openable from the inside to solve this.
So it doesn't prevent theft, but like in real life it increase the chance for the legitimate owner to catch the rascal in action. I believe it would be more fun for the thief too if there was some risk involved in the heist.