This doesn't have a bathroom, it's just a place to sleep and work. Think of it like a workroom, or greenhouse. It was built on a foundation of masonry blocks and 2x4s If you wanted plumbing, you could certainly add it. That's the idea, you build it yourself.

I wonder at what point the structure would become non self-supporting though, in terms of scaling up the size.

I'd actually try going green in one of these - a composting toilet (http://www.letsgogreen.com/index.html) and plumbing that collects rainwater, then drains into a gray-water tank to be used on the gardens.

I suppose standard infrastructure is out of scope.

"If you are considering a canvas dome, teepee, or yurt you should consider building a frameless dome"

For bathroom activities, I would suggest some kind of humanure solution.

looks to me like it doesn't have a bathroom and you are supposed to go outside (or in an outhouse).

I'm also curious how this will hold up against strong weather conditions... heck even light weather conditions

At the low cost for that dome I'd be pretty tempted to stick another one on and divide it in two for kitchen and bathroom.