Great thread, very inspiring. Espalier can be used to put fruit trees in overlooked spaces in order to get more fruit.
Using living (fruit?) trees to create living structures like bridges, and why not, homes too, is very promising, aesthetic, and in a 'good green' kind of way; there is no need to do any painting, not to mention that it's also great for the environment, recycling, etc.
The only setback with building these living structures is the time it takes to completion. If someone or some company were pre-growing and selling these living pre-structure (fruit?) trees, it would certainly be more practical in that a lot more time would be saved. The customer would just buy the pre-structure (fruit?) trees and then have an installer 'plant' them in the desired/planned architecture layout and who knows, this could be the start of a whole new 'really green' industry in the USA.