The trouble with synthetics like phenolic resin, HPL, carbon fibre, etc is that oil is far from a sustainable resource. Wood isn't really that bad as long as forests are managed responsibly. House building (at least in the US and NZ) consumed far more wood than musical instrument manufacture. Much of it irreplacable. Paper and card based composites could be a possibility if you can get enough density. Metal parts can largely be made from recycled scrap. So we're not that badly off. Until you get to valve manufacture that is Mind you, semiconductors aren't that green either.