what do you mean work, i think its pretty much already in the game all it is is swapping your humanoid body for a skeleton enemy, with a cloak on and stat boost and a few new spells, if you ask me editing the vamp and werewolf would be more difficult beacause you have to start from scratch while the lichs animation is already in game just switch things around
I mean how to fit it with lore, how to become a lich, what you can do as a lich, what you can't do as a lich, stat boosts, etc.
also, as much as I love the idea of becomeing differant creatures, including liches, I would hope to become a battle lich with Heavy armor. I don't care if it wouldn't make sense, I want to be one.