Comment by edgineer

There's some neat math that shows how one could send (radio) signals which are undetectable to an observer. Last I read, the research was in specific, purely theoretical scenarios but the idea is that you could send bit impulses which stay within the noise floor. Transmit with a power less than R^2 (in discrete time and ignoring triangulation and you have to pre-coordinate the timing of the transmissions with your partner via pre-shared one time pad and use plenty of error correction) the enemy observer cannot prove that someone is sending signals at all.

Maybe no such techniques could ever apply to the internet, but I'm not sure it's proven impossible. You would need a well defined threat model but if you can show that your enemy is working with noisy data and strictly in the digital space, I don't see why statistical de-anonymization couldn't be foiled.