1) Mages' Guild itself - player joins in one of guild halls, standard Mage's Guild tasks
2) Order of the Lamp - player may join later, involved in Mage's Guild politics, want to ban necromancy (slightly changed concept from Knight's Order)
3) Cult of the Black Worm - player may join later, involved in Mage's Guild politics, pro-necromancy (cannot join both at the same time)
As we know, necromancy is legal in Cyrodiil and even plays an important role sometimes. But we also know that in TES IV it gets banned. What I propose is to have a prequel to Oblivion MG questline, but also a more interesting and interactive questline.
Mages Guild will offer standard for a mage tasks like gathering ingredients or whatnot. These could be creative in many ways, but they are primarily there to give player the exposition, teach him more about Cyrodiil, etc. Again, I am not focusing on these, these are for climbing up the faction ranks, telling their own little stories, etc. But at one point they become not enough.
Inside the Mages Guild there are several factions that exist, most of them are hidden and do not manifest themselves openly. Two of the most powerful, yet opposed to each other are Order of the Lamp and Cult of the Black Worm.
Order of the Lamp are the guardians of the guild who follow the ways of Galerion. They will do anything in the interests of the guild, so I don't want them to be portrayed too noble. Most of them are zealots who put the Guild above anything else. For them, ends always justify the means. Order of the Lamp is a secret organization, but it is also well-known as protectors of the guild. Yet, nobody knows who exactly belongs to it. They want to purge the guild of necromancy for different reasons, but most importantly they believe that necromancy corrupts the guild from the inside, because of the influence the cult has earned. The leader of the organization is Hannibal Traven.
Cult of the Black Worm are the followers of Mannimarco. While technically the cult is separate from the Mages Guild, many cultists are also members of the Mages Guild. While not all necromancy practitioners belong to the Cult, many if not most do. Officially, members of the cult are seen as enemies of the guild (for various legal and personal reasons), necromancy itself is legal. Cult also actively recruits young talents inside the guild. While, these are necromancers and their methods might be vile, they are mostly pragmatics and shouldn't be seen as purely evil. Some members might be complete maniacs, while others seem more than reasonable. Overall, their approach is more balanced and strategic compared to the Order.
Once player reaches a position high enough in the guild, both the order and the cult will be interested in recruiting him. So, the paths divert and player himself chooses one side other the other by the means which would make future change impossible. Most likely they give player opportunity to join ranks, but their test will require player to offend opposition, so only one route is available. Alternatively, player can refuse both, but without their help he wouldn't be able to advance much further in ranks (invisible ceiling).
The focus of the questline shifts to the internal struggle between the two, though player still is able to perform regular guild jobs. The regular quests accompany the inside struggle, which will decide the outcome of it. Player should also be given alternatives inside these quests, which will provide different results.
Somewhere along the way, there will be only one opportunity to betray your faction and side with the other one. In the end, who you sided with and your choices down the line will determine the outcome of it:
- Either Hannibal becomes the Arch-Mage and bans necromancy. The player will receive deepest gratitude from the Order of the Lamp and become new head of the order, while also getting a position on the Mages' Council in the guild. This is more or less canon as we see Mages Guild in Oblivion, though the events are taking place slightly faster due to player's involvement.
- Or another possibility is victory of the Worm Cult. Order of the Lamp is crashed and destroyed, necromancy is legal and Worm Cult positions inside the guild are strengthened. Player becomes new Arch-Mage and is also given a high rank inside the cult. Might even receive a thank you from Mannimarco himself