Idk the state of the art for forensic stylometrics or the precedents but I would be surprised if this hasn’t already been presented as evidence in many (most?) notable jurisdictions. Not definitive evidence but supporting evidence. So far from being declared illegal, it’s probably mostly established as a tool for law enforcement.

Meanwhile gangsters or nation states are probably already working on automated deanonymization and blackmail at scale, but will target the dark web before the public one. Not sure any of this stuff is that changed by the advent of deep fakes and llms tho, probably just boring classical statistics does ok?