ok, all 6 SoD is 120, plus all 6 Granite Skin is 450 plus the base 100. thats 670 maximum hp that can exist right?
6 void dragons is 48 hp per turn is 13 or 14 turns one can live, this goes down quick when you add in the fire Reaver card i saw, and add in voidstalker for 5 each thats 30, it gets to be just a few turns quick. balance normal creatures on the board and possibly neurotoxin, you need some defense against it. i think most people will take one or two balms the way they take one or two purify, and one or two miracle or eternity.
im leaning toward a split between purify and SoD/granite skin, or a permanent that increases max hp, but not current hp each turn, maybe a permanent with a high activation cost to remove wounds. i think something that gives you max hp and is disposed is covered by sod/stoneskin. i think a permanent that removes wound tokens is a good idea, but that wound mean reducing max hp would need to be done with wound counters instead of lowering max hp directly.
a permanent that raises max hp by 3-6 per round is not out of the question, if those max hp cost a few quanta a piece anyway.