Have you considered Frostmourne or Shadowmourne (or approximations thereof) for the ISO Enter novelty? I guess something like that might have IP implications?
I like the novelties overall, but I have to say I prefer the R1/R2 Unholy rune skull design over the more abstract bottom row one. I wish the skull design were available on the bottom row too, at least for the 1u keys. Alternatively, what about a bat/gargoyle-looking thing for the bottom row icons, to match the original Unholy rune design? Here's an in-game screenshot from the original WotLK client (peak wow amirite).
The legendary weapons' details are very hard to replicate in double-shot restrictions and reducing its edges/details IMHO not worth translating into. Plus, personally I wasn't a fan of having any kind of weapons (be it blunt, sharp or firearms) image on any ANSI nor ISO Enter key. IP implications-wise is also true.
I love the idea of R4 (bottom row) 2x 1u keys being the unholy (green) skull instead of unholy rune, will try to implement that.
There are much more specific & iconic DK skills that I really wanted to put into the novelties (Death & Decay as you mentioned, also many more that I've been a fan of like Blood boil, Death/plague/frost strike, Unholy strength, etc.) but I want to just focus on the main runes (blood, unholy, frost) theme for now.
Thank you konstantin!