Before I did that, in an effort to contain the thick clouds of concrete dust produced by the diamond bladed circular saw slicing through concrete, I built the wall that closes off the opening between the home theater and the new laundry room. Photos taken 1) from the home theater, and 2) from inside the laundry room.
Once that new trench was filled with concrete, I could build the part of the laundry room wall that separates it from the new guest bathroom. The new wall is flush with the back wall of the laundry room, and provides more area for the guest bathroom, needed for a new vanity (and some storage). That new wall segment will also house a new electrical subpanel, replacing the old, physically smaller subpanel box that was in the old, smaller laundry room (it's about five feet to the left of where the new panel is). You can see the new panel in this photo, just sitting in place for the photo. The old smaller panel, besides being cramped, is located behind where the washer and dryer will be going, which is a no-no. The area in front of electrical panels has to be open.
You might also notice that the door leading to my only current bathroom is now behind a stud wall. That door, and the whole wall it is in, will be removed (soon), and a new pocket door will be installed between that bathroom and the home theater (which will also serve as the guest bedroom). Until that happens, access to the bathroom will entail sidling between the studs. Good thing I'm thin!