David Sameshima left it to me to comment on his photoset today.
To me, the most interesting thing about the work you see in this set -- and it does appear that workers were on the job Sunday -- is the exposed framework at the top of the ballpark. Some concrete that was in front of this framework has been removed, exposing the steel behind it. I suppose this is what Cubs spokesman Julian Green meant when he told me there would be "structural work" going on, on the outer facade of the park. That's the reason the marquee was removed, for example. You can see what the finished product will look like in this rendering (click to embiggen):
Also of interest, the "cooking stains" on the bottom of right-field video board. somehow i don think they had planned for this to happen wonder if that food-preparation station will be moved or adjusted so those kinds things in future.
Finally, the last three photos of the set are really cool, I think, showing an unusual light bouncing off the underside of the steel floors of the plaza building.
We'll have more photos here later this week.