Out of curiosity, why would it be plumbing? There should be enough capacity to handle both fresh and black water, considering the high occupancy of typical office buildings.
I wonder what causes these buildings to have such restrictions on plumbing. Maybe it's like elevator shafts where they eventually take up a lot of space if the building is very tall.
Conversely, adding more toilets, for example, may also pose a challenge. My dad helped design the plumbing system for a rebuild of a football stadium. One of the final tests was to have a bunch of volunteers go to every sink, toilet and urinal in the building and turn them on / flush them simultaneously to ensure that water pressure stayed high and the drain pipes didn't back up.
Adding more toilets in a building not meant for them can be a big deal right after lunch / around "busy" times... Some may not be able to flush or overflow if the pipes can't handle the extra activity.
Who instituted the limit? Was it in the lease terms, city ordinances, or something else?
This means you couldn't chip up the concrete slab to place new pipes, the way we could in e.g. a strip mall. This is an understandable limitation, because the integrity of slabs is important for tall buildings.
However, this wouldn't be a limitation in a residential remodel. They aren't going to mess with the slab or the pipes in it. They're just going to lay everything over the top of the slab. If the new toilet is 40' from the utility shaft, that is 3" for the pipe plus 5" for the fall. Add an inch for the floor itself. Average residential ceilings are much lower than average office building ceilings, so there is definitely at least 9" to spare.
Retrofitting all that additional plumbing is expensive.
Toilets are obviously a different story. But as long as no one is shitting in their kitchen or bathroom sink the water flow post-usage can in theory be managed.
I don't think it's a timing issue. The issue is that the fresh and wastewater plumbing simply doesn't exist in the places you'd expect in housing, so there can be a significant cost to adding it, beginning with just figuring out where you can run it through the existing spaces.
A holding tank and whatever pipes then are used to empty it are still plumbing, and even more complex than regular plumbing, unless you are suggesting that people would haul their own waste out periodically.
Also recall that wastewater pipes need to be at least slightly angled so that they drain properly using gravity, further constraining their potential paths. This can be quite difficult to design even when remodeling a regular house.
If you need intermediate pumping stations or holding tanks due to the height of the building, those could be inside adjacent to the outside pipes.