Welcome, Abessive, and I love your Plektoi. Thanks so much for bringing them over to the forum. I’d also be interested to hear how people first visualized/imagined them on their readthroughs.
I don’t think I’ve shared his before, but this was the original draft sketch I was sent of what would become the XoR cover art:
If I’m honest, its abstraction appeals more to me than the final cover art did! 
But Abessive definitely has the most book-faithful version, and my fave so far.