You could certainly force the bathroom placement with the wet walls. Code is code, and space folding does not exist. So if you only allow for 18” of drop on the

You could certainly force the bathroom placement with the wet walls. Code is code, and space folding does not exist. So if you only allow for 18” of drop on the pluming then all the drains have to be within fifteen foot radius of the sewer line. And the floor beams will limit that further. That said, the responsible thing is not to convert the whole building but make a sandwich of retail ground floor, residential above, then commercial, then maybe real estate top floors. Weight carried low is fewer failure points for the building.