With pex plumbing and high velocity HVAC, you only need to run small, flexible tubes through the framing. It should be relatively easy to print small, flexible holes for tubing. Agree that traditional ductwork and copper pipping would be hard to accommodate.

Drainage is the hard part. The pipes are larger and require you to cooperate with gravity.

Sewage is absolutely NOT a problem for a single story houses. No large sewage pipes are installed in the walls of all single story houses.

Sometimes they are. My house is single story and has sewage pipes in the walls. Regardless of whether that is a requirement, the pipes have to go through some part of the structure to get to the outside, regardless of whether that's a wall, floor, foundation, etc.

It’s possible but only done for convenience where it makes sense to, not a requirement for new construction since you just put the pipes in before the pad gets poured.

Your toilet pipes are inside a wall? That’s pretty strange, toilet drain pipe is usually 3” dia. Are there 90 degree bends? I don’t understand how or why you’d put a toilet drain pipe in a wall when the drain pipe is in the middle of a bathroom floor, not in a wall.

Are you sure you aren’t thinking of sink drains?

Yes but GP said large pipes, e.g. for a toilet or the main pipe that connects to the municipal sewer. In a single-story house these would be under the floor. Pipes in the walls of a single-story house would be sink drains or vent pipes, and are narrower.