Hi there!
I really like the idea of shurikens circling around yourself. In combination with Ethereal Blades (pierce chance) its fun but it kinda lacks something special and sometimes positioning feels weird. So I wanted to give it a try and describe a possible rework:
Make Blade Shield into something like “Blade Storm”. Instead of individual shurikens flying and hitting enemies, change it into a storm swirling around yourself, so everything that stays inside it gets hit by shurikens per second. So if I have +4 additional shurikens, enemies get hit 5 times a second (+on hit effects). To make it interesting with Ethereal Blades, maybe it could increase +25% hit frequency per point, or make it a new node for Blade Shield so fully maxed it would then hit 10 times a second instead of 5. If damage scales too high, decrease skill damage per point, something like -10% or so. Applying ailments this way could be so great!
Another interesting addition would be to add Area tag to Shurikens when Blade Shield is allocated. With the addition of increase Area affixes, it could scale larger in size. Maybe even add new affixes to Idols for this.