In 2003 Lukasz Kos, a masters student at the University of Toronto's School of Architecture & Design, took honourable mention at the OAA awards for his Muskoka, ON. treehouse, an elegant slatted structure that scales the trees and lets light radiate down it's core.
More recently, Joel Sherman of jls Design produced his AIA award-winning Steel Tree House in Lake Tahoe, CA, a sprawling residence that is cleverly engineered to work with snow loads and sloping terrain. Then there is Marcio Kogan's BR House in Araras, RJ that was built up to the canopy, and allows trees to puncture through the roof at points creating a contemporary elevated living space.
It seems that idea is less about reducing the ecological footprint, and more about the treehouse as a relic of childhood that is virtually extinct in urban settings. By resurrecting them on a very grand scale in a more sylvan setting, these treehouses are the ultimate in treehouse design, and no doubt the owners are the most popular kids in the forest.