Making a good Necromancy mod will probably involve some elaborate rituals and quests to obtain ingredients, etc. for animating a corpse. On the other hand, who's to say that there aren't other interesting spells from this school (i.e., something besides creating an undead servant) that we simply haven't heard about yet.
For example, if you look at the history of necromancy IRL, a spell like Clairvoyance fits with a lot of descriptions of medieval necromancy, it would just require something like the remains of a person related to the quest as a material component in order to cast the spell. In fact, that could be a really cool way to balance the power of the Clairvoyance spell. There could be other interesting takes on this, as the concept of necromancy need not be limited to the descriptions in passages from previous TES lore books.
This was a huge missed opportunity in Oblivion because all the Necromancer NPCs we encountered had basically the same arsenal of spells as most of the other spellcasting NPCs. IMO there could have been a deeper, much more interesting culture for this faction.
Historically, in ancient times, Necromancy was a sort of divination involving corpses or summoning the spirits of the dead in order to seek guidance. Later, in medieval times, necromancy was considered a form of sorcery involving summoning demons or spirits (which in Skyrim could translate to Daedric beings) for purposes of:
- reanimation of the dead
- food and entertainment,
- to drive people mad
- to inflame people to love or hatred, to gain their favor, or to constrain them to do or not do some deed"
- conjuring a mode of transportation
- identifying criminals,
- finding items
- revealing future events.
some TES lore about Necromancers
http://www.imperial-library.info/content/morrowind-preparation-corpse
http://www.imperial-library.info/content/morrowind-arkay-enemy
http://www.imperial-library.info/content/morrowind-legions-dead
http://www.imperial-library.info/content/oblivion-black-arts-trial