Now here's a thought.... bamboo is apparently a pretty good material for frames but the limitation must be the joints and how to transfer the stress smoothly from one tube to another. Traditionally (!) bamboo grows in straight lines but I'm thinking that with cell culture it might be possible to persuade a bamboo plant to grow and fill a mould, somewhat like we are beginning to grow human cells in vitro for medical purposes. Just imagine; the whole frame would be one continuous structure with no joints and everything 100% chemical-free. You could even persuade the frame material to grow around and integrate with the BB and headset.
Anybody care to speculate on this? Got a few hundred thousand quid you'd like to lend me to test the theory?