why not just grow a house?

you could certainly still integrate old architectural ideas, you could have conventionally constructed (or slightly less than conventionally constructed) room dividers, and you could produce a multi room layout with proper planning, not to mention, say you build around an existing plant (tree) you could build, say, a treehouse, above the lower structure, and have a second story, it asks for more creativity, but the rewards could be great.

and I know, even if this worked it wouldn't be widespread for another three or four generations, but getting started now could be epic.

 

It is all good ideas, Dave.
But it still does come down to "man" hours and the cost of those "man" hours.
It costs a hell of a lot more to do the modifications or ideas you suggest, than to put up a conventional eco-home (what with planning and building regulations as they are and will be for the forseable future.)
Red Tape: http://www.communities.gov.uk/housing/
Shame really.
I don't have to add these boring details if you wish.
This being a dream after all - lol.

 

that's why it has to be a generational project. it's not something that will happen in any one lifetime.