The thesis material and findings, shared earlier on bitcointalk, seem pretty solid. He does admit he hasn't cracked more innovative mixers, but given than the majority of mixers out there use the same algorithms, if he's right, then any coins ever mixed can be traced back to original source. And past mixed txs cannot be retroactively fixed apparently.
The full article: https://bitcoinnews.com/exclusive-college-student-claims-to-have-cracked-bitcoin-mixing-services/