True this needs to be solved.
Still, Monero is just a crude hack compared to zerocash.
You are assuming that it can be solved. I am skeptical.
Have you read the rest of the Zerocash paper and process? The crypto is seriously cutting edge. I'm educated quite highly in related areas and I can only understand at a higher abstraction level what they are doing. Zero-knowledge proof is very impressive. I'm sure they'll be able to leverage something similar to solve this issue.