At this point, I'd simply love to know what's causing it. It's not simple light bleed, we know that because it's separated from the edge of the screen. It doesn't seem to be adhesive, because it's not going away but seems to be getting worse for some folks. And it's widespread enough (if not on every machine, just perhaps too light on some to see it particularly in bright lights) that it appears to be a design defect.
I'll toss in the bit about the apparent distortion in that area of the screen, just to confuse things, because what could be there on the screen that would both distort with pressure and cause discoloration? Now that I think about it, I'll have to remember to check if touch/inking goes all the way to the edge (on the other side of the line), to see if it could have something to do with how the digitizer is fitted to the screen.
It's a mystery, for sure. Biggest question is: will Microsoft be able to fix it, economically? Or will they just write it off since it's not so noticeable on all machines unless you actually look for it?