I don't know how you could make it, but If I got a suggestion, the one I would give you is to make it EXCLUSIVE.
What I mean, is that not many people could become a lich, a force to be reckoned with. There should be just few people, and the lichdom "curse" cannot be spread too all the mages living on the mmorpg.
There should be some shrines, guarded by great monsters\lich where there are some hints about it; or where the procedure itself can be done, because there are paintings\writings on the wall.
The cute thing, is that you can't find the shrine alone. All the people trying to find hints about lichdom should spend a great amount of time by figuring out how to find these shrines.
Becoming lich is serious bussiness, you know, so before starting the process you should find a way to guard the lair where you are confined during the time you can't use your main character, (24h-48h?).
What do I mean? I think that some people would roleplay a paladin type of warrior, and they would try to wipe the evil infection from the world.
As soon as the process begins, these paladins should receive an hint by their gods that something bad is going on in some place ( that place should be highlighted in the map, but not in a precise way... it should be around, maybe in 20-30 km proximity).
The paladins would so try to avoid the lichdom to become lich.
If you fail to become a lich, because the paladin kills you, game over. You must remake your own character, there is no resurrection.
If the paladins kill you, the shrine will become to collapse, and with it all the evidence on how to become a lich.
The lichdom should be related to the shrine itself.
And shrines should be not many (maybe 10-20 on the whole world?)
Well, I think I've gone too far. But anyway, add lichdom to Elder Scrolls Online and make it so that not everyone can access it, but just a limited amount of people!
