I didn't make this, credit to Kathranis.
I did some sketches last night of some potential Ethereal customization options. Might as well post 'em here.
Customization options here are energy color, energy trail styles, energy trail color, bindings, and binding colors.
And this was really lazily done, but I was thinking about the possibility of them having unique geosets for their different armor types, so that the armor would look completely different on them. Based on the same concept that allows armor to look torn up on Forsaken...
Iit's kind of a crappy example since I just grabbed a random transmog look off google image search, but the idea is simple enough.
Edit: Here's another I whipped up. Paladin.