If you use Fossilize with Fragmented Shield and the obligatory Volatile Armor + Cauterize on a medium build, I think you will find magicka sustain too tight without wearing something that gives you magicka, such as Torc, Eternal Vigor or perhaps Engine Guardian or Atro mundus. I think Shacklebreaker wouldn't be enough. That means you'll probably end up throwing out Fragmented Shield and you'll rely on Fossilize for the Minor Brutality. This would be my kind of build, but lots of people cringe when you tell them you're not using Fragmented. Also the needed magicka sustain in some build variations is likely to indirectly compromise your weapon damage. Heavy armor passives have an advantage in that they help restore magicka.
Having played my own medium build a little longer, I have mixed feelings. My choice of Coward's Gear is situational. Great when you're the wrong side of a zerg, not great in duels. I'm currently trying Engine Guardian instead of Bloodspawn and I think it's better.
Fossilize + Selene seems like a nice idea, but I think you will either not run Fragmented or you'll have to find magicka somewhere.
What if the real deal was adding Ring of the Hunt fir extra mobility and in combat speed?
Anyone tried it out?