Keep an eye on phiTame. If you watch the videos on my nexus page you will get an idea (i think I talk about it in video 2) what I am planning to do. If you play the current release you will get the general idea, though conjuration will involve a soul gem trapping and ritual summoning mechanic where you have to defeat a special "boss" type sequence for a given "spirit" or undead/daedric creature in order to add it to your list of summons you can command.
So far it is coming together really well. I expect a release within the next few weeks.