I haven't read this entire thread, but if we are concerned about the directed graph of transactions (represented by the block chain) being visible for a long time, then what about using self-destructing data for the block chains that will expire and erase themselves after a specified time (such as a couple hours) or after a certain number of nodes have confirmed the transaction?  For example, I stumbled upon this scheme called Vanish - Self-destructing digital data which uses on-line distributed hash tables to store and gradually degrade the encrypted data and key over time?  So basically have older block chains automatically vanish after a certain time -that way transactions could be verified in the short time span, but would be destroyed in the long time span...thus preventing the authorities or whoever you are worried about from reconstructing the block-chain and use that directed graph to determine your identity. 

Anyway, I'm just brainstorming here, not giving any solutions , and I don't totally understand the internal workings of bitcoin either , but maybe someone out here in the forums is clever enough to figure out some scheme using self-destructing data to protect anonymity.