Foam is in. It's starting to look like a house!
I just got the subfloor sprayed with foam insulation! Freedom Foam Insulators came early morning and the whole thing was finished in a few hours. They were currently set up with open-cell foam, so instead of paying a $350 fee for him to switch to closed-cell, I opted to just use the full 3.5" of open-cell foam in the floor. For the walls and ceiling, I will give him more notice so he can schedule me in right next to another closed-cell job, so I can avoid the switchover fee.
Once the foam was sprayed and given a minute to dry, they came through with a saws-all with a massive flexible blade, and shaved off all of the overflow foam to the height of the studs.
Now time to start sheathing and wall framing! This step will take a little longer than normal, because I have to cut holes in the plywood sheathing and framing base plates for all of the various plumbing and wires I've got coming up from the floor. Once finished, the walls will also need to be lifted into place carefully (and wires threaded through holes), which will require help from a few strong guys to get done quickly so I don't block the floor space around me which is used daily by forklifts in the Creative Edge warehouse.