1. All crypto will be cracked eventually, it is just a matter of time. First we have key length requirements increase over time:
http://www.keylength.com/en/compare/2. Next we have IBM's head of research for quantum computing (with a $3 billion budget) expecting that quantum computing will arrive in 10 - 15 years. All the crypto-currencies to date use crypto that can be cracked with a sufficiently powerful quantum computer. May not happen in 10 years, but eventually it will.
Maybe if there is a way to re-encrypt the whole blockchain with a stronger encryption over time, past anonymity is not endangered by computational advances. Just an idea that flew in my mind.
It has already been seen, you can't increase the encryption strength. Somebody stored a copy.