A quick and easy thought is to create a division of sorts when considering an Npc/Monsters backpack loot. One division is, already, granted upon death. The second division would be a static loot; built in just for the skills snooping/stealing. This would give a great reason for the EVO staff to create a functioning Thieves guild [run by NPC's] which would have its own contract [Mark] system. The Mark contract would come in two flavors: kill or procure.
Assassination contracts are obvious, and the rewards should be similar to that of Monster contracts. However, the bonus loot tossed into your bank box should be useful to a rogue. Decoration that suggests rank, or accomplishment. Rare, usefull, dagger any one? Or most importantly, items which build on the whole. For instance the second kind of contract requires the thief to procure something. Simple contracts should be one or to items which are then handed in. Harder lists should mimic the Hag Quest, yet be rogue like in nature. Other types of contracts could require items only found on bosses, who have been snooped, and then stolen from. Perhaps even snooped after the boss was killed? Anyways I think you get my point Expo.
Add more fun and useless Deco, small amounts of extra gold, and Keys [think mundane commodities, to rare items; secreted away throughout the realms which require these keys in order to gain useful loot] These keys are found inside of a snooped NPC's/monsters backpack, then stolen, and used to open locked chests which are hidden everywhere and nowhere.
(remember this idea requires static loot to be place on a mob, prior to its death. [Think artifact system]
My personal choice would be to allow stealing in Fel; thus reestablishing snooping as a needed skill.
Last, snooping could be the trigger mechanic for randomly filling static chests, and other containers, inside all of the dungeons we so love. Do not snoop if you are not able to defend yourself, however. Why you ask? Because a side effect of snooping static dungeon chests could be the spawning of random tough monsters/guardians. {think of the spawns for treasure map chests, only tougher versions: more hit points, a higher to hit ratio, and other pesky [fun] stuff like that.
That's what I got for now, I'll think about it some more.
--Sturger--
P.S. 10 seconds to think up, 40 minutes to write, proof, and spell check... yesh. So much for a quick reply.