It depends on the corpus. Stylometry (which is the actual name for this, not 'forensic linguistics') can be surprisingly accurate if it has a good selection of text to work with. How hard do you think it would be to crawl public facebook posts, reddit posts, posts to various hacker forums, and build a corpus large enough to connect the dots? I am betting it is a lot easier than most people think.

Next steps will be application of GANs and similar tools to stylometry to either give your posts a linguistic signature of someone else or to just remove enough unique data points to obscure the source.