I'm not sure if someone has already posted about this but...
I think it'd be cool if there was an update on the battle circle. It's been a pretty consistent feature throughout the games development and this could be an opportunity to visually attract new players. Perhaps something with more depth, more static or moving particles throughout the entire sigil to enhance the magical aspect of a battle, perhaps make the lines within more seamless. I think a more vibrant display of health would be cool.
Also, It's nice how shadow magic is displayed as a stat on gear or as a shadow spell, but what about introducing gear that actually looks like shadow gear. Maybe as a skeletal key boss drop or as any general final boss drop. It would be kind of similar to the design of our shadow pips and its mini aura yet distinct to the world we would receive it in. Perhaps it could be crafted and have a visual feature distinct to each school.
Cool concept. They’ve done a good many graphic changes since the inception of the game so all of what you’re saying may come to fruition. As for the skeletal and dark stuff- it already exists as far as stitching goes. Umbral gear as well as many others that make for great “dark” themed stitches.