Nice theories guys!
I've had this theory bouncing around my head that the Willshaper was going to be Lopen. I totally missed the point about the "uncut gem". Which I think would still fit Lopen.
What made me think that Lopen was the Willshaper was how he sorta just willed himself to absorb stormlight. I know that is not really concrete evidence, but just a thought.
Also Uncut gem could describe him since he really is a unique character, and is some what "unrefined" by Alethi standards.
*Shrugs*