Stylometry is an old hat technique; you can assume that intelligence services around the globe regularly apply it.
(Statistical stylometry is a little newer and more rigorous than manual stylometry, which essentially involved a human being's judgement call around the similarity of documents.)
I don't know, but it wouldn't surprise me if someone has tried to apply ML to stylometry. Statistical stylometry is already petty effective, as demonstrated by this site.
(Statistical stylometry is a little newer and more rigorous than manual stylometry, which essentially involved a human being's judgement call around the similarity of documents.)