IMO Luck was taken out because it's so damn messy. *lol* Personally I envision Luck coming into play whenever a random number is requested to determine an outcome. Akin to a dice roll in paper and pencil RPGs like AD&D.
How many gold pieces are found in a chest? Did an attacking skeever connect with it's bite? Were five goblins waiting around a corner to ambush the player or were there only two? Were some or all of them asleep? And so on. Not sure this would be possible in an addon though.
Of course the developers can go right to the root and have luck affect the random number generator. But even that is tricky. There will be some rolls that they may not want to have Luck affect. Or maybe they'd have to introduce Good Luck and Bad Luck. IMO this can be a lot of extra work for something the player never appreciates. That is... if they manage to dodge three attacks in a row, the game doesn't say, "You were very lucky there twice and very skilled once." From a design perspective I liked the Luck stat being gone and leaving the dice rolls to fate.
Wow. Really rambled there. Sorry!

So for Skyrim... maybe it would be an Active Effect that provides a very small boost to magic resistance, armor, health regen, magicka regen, and Speech.