I like the idea a bit, although I have a few thoughts:
First, if your primary goal is uniqueness or individuality, I definitely think that the bones on the cape look better with the whole "bulking up" shoulder-bone-yard idea. The "bulking out" compliment each other and keep things from looking.. like they are lacking something.
I get the look, it looks very "Viking" with the bulked up shoulders, reminiscent of a barbarian you'd think of with a huge bear/wolf cloak. But instead of mere animals, Nagash has bested and skinned death itself. The concept is there, and cool. I also think people might be looking at what you have mocked up as "bones" when realistically you're just using those for filler mass, and you plan to cover them with more of a full bone-pit style coverings, rather than using "giant bones" the size those mock ups are... right?
Because realistically, in my mind, there aren't quite as many huge bones to drape across him, and I think it doesn't quite get the point across. With huge bones in substitute for those
noodles on him currently, it looks more like he's a giant/dragon hunter, with trophies of his hunts. But that's less the intention than screaming pure "DEATH". And I assume it will be more of a look like a bone-pit/the linked picture you presented, which is far more amorphous. That's the look I think you should go for, at any rate.
In keeping with that idea as well, I think the bones draping down the robes are an alright idea, but perhaps not as..
sausage-linked bones, but rather more like I mentioned before, with more "Whole" skeleton parts of the much smaller lives he commands in unlife. Like with full rib-cages or such, maybe even a skeleton trying to claw/crawl up his robes or such.
At any rate, these are the directions my mind when when I saw your inspiration/ideas. It might be a bit over the top, but I think it would be much cooler.
As for the helm, I agree with
@Adam_Barrow that perhaps less could be more. I'd toy around with it to see if it perhaps looked better at a certain ratio (As long as there aren't 8 equidistant points!). Alternatively you could in different directions? The old Nagash presented by
@wheeljack, as well as the new Neferata, have those "bone surface" style hats.. which come to think of it is fairly similar to Nagash's current pope-hat you hate. One of the only really "Slavic" themes I noticed when looking at period-typical helms was something like a
face-mask. Which could be cool? But I don't think it's the style you're going for, nor what should be on Nagash. Plus it's probably far too Stormcast for anyone right now :ghost: But death-metal-evil crown works, for sure.