Mostly I’d just like to see more heavy armor chestpieces with neck covering, and heavy legs with the outer skirt a la the HotW set legs or Vigil legs (ideally without bare thighs like the latter, though).
Circlets/crowns for more castery-focused guardians would be pretty slick, too.
Actually, now that I think about it, there’s some existing armor I’d really like if it were tweaked slightly—first and foremost in my memory is the temple heavy set, which is hard to match to other stuff because of the stupid skulls around the collarbone. The way it flares out a little at the waist looks cool, IMO. The ascended armor is kinda in the same boat with its medallions around the collar, but there’s other excess visual noise that’d be harder to tweak, I think.