I really love playing with necromancers\summoners in any MMO. ESO is an amazing game , having a necromancer class would be fascinating .
The necromancer should be able to summon minions , siphon\leech foes health to heal his ( vampire ) and to transform into a lich\ghost form.
You could add a necromancy skill line instead ( Daedric Summoning is not a real summoning one as it contains only 3 minions).