One thing I'd like to see is merchants refusing to do business with you if you have Skooma or Moon Sugar in your inventory (except for fences, drug dealers, and Khajiit caravans). Could probably also run the risk of them calling the guards and giving you a bounty based on how much you have. Also, you could try to make it illegal to pick up Skooma or Moon Sugar (to avoid the drop-trade-grab exploit).
Though the other day I had a big laugh after a lengthy Morrowind session (New graphic mod pack is amazing) when I later played Skyrim and reflexively dropped out the Moon Sugar I had just purshased from some Khajit before trying to talk to a merchant in Whiterun. I immediately realized how silly I was but before I picked it up, two NPCs started arguing over it

My take: This isnt a desirable feature to implement, though. It worked that way in Morrowind because there was no way to script the merchants back then to refuse to buy specific items. We have better solutions now. Simply flagging ALL Moon sugar and Skooma as 'stolen' through a script or some such would be a MUCH better solution. You dont want the player to have the hassle of dropping items when a flag gives better results (merchants wont buy it, guards will confiscate it if arrested; perfect).