The IRS has paid out millions of dollars in a failed effort to deanonymize Monero transactions without a lawful subpeona. Thus, a lawful subpeona is still required in order to unseal Monero transactions in the US, I.e., to compel the production of a view-only cryptographic key.
The video was posted elsewhere I think. Basically, if you view enough of the residual ring inputs you can link them together. This is not quite practical yet but assuming wide adoption of XMR chain stores, etc, would be able to do this attack.