Forensic textual analysis predates the internet, actually, and I can say with near certainty that someone out there is working on this right now. (Probably the CIA, and/or another agency involved in analyzing communications between persons of interest).

Back in undergrad, I was involved in a project that used textual analysis to surmise authorship of "anonymous" works of fiction from Shakespeare's day. Additionally, the authorship of a lot of works attributed to Shakespeare is often called into question, and so we tried to map for consistency or inconsistency in his works. (Spoiler alert: he turned up pretty clean; he -- or at least someone using his name -- is most likely the author of his works).

Now, obviously, this project was a bit high-touch and involved a lot of attention lavished on a single body of work by a handful of presumed authors. But that was a long time ago, and I'm sure that the technology has grown more scalable and sophisticated by now.