I refuse to go plumbing for trouble when I am unable to see the full context of the situation.

The neighbor's design is a typical suburban infill lot concept, just a little stretched.

The seller's design seems to be designed for the site (it was designed by an architect for someone and someone's site somewhere). If you notice, it has a very strong view axis towards the Northwest. A lot of the plan's concept revolves around views and having access to them throughout the house. The opportunity for value level seems appropriate for the high end of this region.

So if this seller's design indicates assumptions about your site, your proposed plan does not meet those well. But, with the symmetrical concept and framed view, where I wouldn't blink an eye is if I saw it on an urban infill lot on the intracoastal in Florida.

Jumping in on the steam shower spec, since that's a different animal than a regular shower build: the ceiling needs to be sloped (not flat) so condensation runs down the walls instead of dripping on you, and the whole enclosure — walls and ceiling — needs a continuous vapor barrier behind the waterproofing, not just the standard shower membrane. You'll also want a fully sealed steam door (floor-to-ceiling glass with a tight bottom seal, not a standard shower door with gaps at the bottom) or the steam just leaks out and the generator runs constantly trying to keep up. And make sure whoever sizes your steam generator is calculating off the actual cubic footage of a 4'x6' enclosure with your ceiling height — undersized units never get hot enough, oversized ones short-cycle and wear out early. Worth confirming your contractor has built a few of these specifically, not just standard showers.

I grew up in a bungalow that originally had two bathrooms; they were outside beside the barn.

" . . . should have had more foresight."

Or hind sight?