Just a couple of ideas I had of a dlc of useful master level spells one for each school. For hardcoe mage characters. each involving a small quest to get each. for like 200ms points range maybe.

Mind above Matter (bad pun since you'd be off the ground but it had to be said also everytime I suggest levitate people think I mean flying) - master level alteration spell

Using telekenetic powers on yourself you hover slightly off the ground (like the vampire lord in Dawnguard), so you can't enter citys except by the doors or get to unavailable areas, consuming magic per second, makes you go as fast as a werewolf run if moving while hovering, (better way for mage travelers with low stamina and high magic pool to travel) also faster than mounting or dismounting a horse since there is no casting on horses.

Supreme Resurrection - master level restoration spell

Allows you to resurrect dead npcs or enemies. Enemies being resurrected that would conflict with the questlines would be listed as either resistant to it or too high a level for it to work. You could save shopkeepers that get stupidly killed by vampires in dawnguard and dragons. Also a change to regular zombification, resurrected zombies no longer turn to dust when killed. I've had adrianne avenicci killed about 10 times coming into Whiterun then a vampire resurrects her and she turns to dust. Reload. Very annoying. So you wouldn't just kill them and resurrect people all day for fun you could make it cost a soul gem so you don't go on killing sprees then revive everyone.

Tornado - master level destruction spell

svcks enemies into a vortex in a funnel area, basically like the blizzard spin animation but a smaller area and see some sort of high speed wind effect throwing them in the air and hitting walls or thrown into the sky, taking falling damage. Hits enemies and friendlies alike so don't cast it in town lol.

Army of Darkness (lol yeah I know) - master level conjuration spell

Only works on humans, corrupting the souls of the dead creates Area effect spell starting from the caster, raising their spirits to fight for you, for simplication they could just make an ice wraithe type model http://elderscrolls.wikia.com/wiki/Ice_Wraith come out of the bodies and start melee attacking enemies. When the 60 seconds are over fills any black soul gems you have empty up to how many spirits there were.

Lost memories - master level illusion spell

small area spell that makes NPC's and guards forget crimes they had seen you do, also allows you to retry pickpocketing, and removes bounty if you all witnesses have forgotten instead of having to murder everyone.

Feel free to share feedback, I'm sure none of these would be likely to happen but they could add a little bit of versitility and originality to the current set of spells in game.