Managed to snap a picture of the plaza work going on along the Canal St side. They've totally demolished the concrete deck and they're working on removing the old steel beams. Lots of pipes being held up on temporary shoring while they do the work.
I thought there were Union Station tracks directly under the south plaza, but it's actually just basement space. The north plaza does have tracks beneath, so the work on that end will require some Metra coordination. Explains why they haven't done any demo on the north side yet.