Well the contractor came over today and basically told me to use an increasing thickness of thinset to angle the wall tile out to keep the wall tile square with the floor tile in combination with slowly angling the tile to match that line. I've got a tiler coming over on the weekend, I guess...
I'm in the middle of a new bathroom install and have hit a bit of a snag with a bathroom wall being out of square. This bathroom was just framed from scratch, and as you can see from the attached photo one corner is pretty badly out of square. I already had to have the contractor fix the studs...