Skyrim already has a lot of the mechanics you posted, and it's very easy to break that game using them.
I vote for keeping current system: Sorcery=Seath Magic(a form of dragon magic), Fire Magic=???(possibly the daughters of chaos, or everlasting dragons, only other creatures seen using fire apart from demons and pyromancers), Miracles=God magic.
And likely some other unique spells created by specific people (such as Vinheim, Dark and Oolacile sorceries, Carmina's pyromancies, and Havel's miracles)
It seems necromancy/summons don't really belong in Dark Souls world (even though i like Conjuration)
Other dragons seen using magic are the everlasting dragon, with those shapeshifting stones that seem to grant their users part of his power; and Kalameet, whose lore leads to believe that he could be more powerful than he is in gameplay.
I vote for keeping current system: Sorcery=Seath Magic(a form of dragon magic), Fire Magic=???(possibly the daughters of chaos, or everlasting dragons, only other creatures seen using fire apart from demons and pyromancers), Miracles=God magic.
And likely some other unique spells created by specific people (such as Vinheim, Dark and Oolacile sorceries, Carmina's pyromancies, and Havel's miracles)
It seems necromancy/summons don't really belong in Dark Souls world (even though i like Conjuration)
Other dragons seen using magic are the everlasting dragon, with those shapeshifting stones that seem to grant their users part of his power; and Kalameet, whose lore leads to believe that he could be more powerful than he is in gameplay.