Seizing the DirAuth wouldn't achieve anything useful: all the data that the DirAuth has access to is a matter of public record (literally, the role of the DirAuth is to collect that data, sign it cryptographically and vote on it).
A group of nation-states looking to attack Tor this way would need to stealthily subvert a majority of the DirAuth, and manipulate the network consensus in a way that is both hard to detect and allows them to deanonymise users; that's very far from trivial.