On drawing black:

LCD glasses that "darkened" at specific points do have the problem that those spots would be blurry, yes.

But if the spots are big enough, then they will create solid block spots at their middle. And the display can then "fill in" the darkened blurry spot proportionally with the "same" pixels from the camera, altering the ones it wants.

It would look bizarre for people looking at the person wearing the glasses, with strange black dots flitting across their glasses... And the syncing would have to be perfect (very difficult).

But it's an engineering issue, not a fundamentally physical one.