First come the programs which generate fingerprints from writing samples. Then comes the corpus of known author fingerprints which can take a submission of arbitrary content and turn it into a series of authors and confidence values.

Later, someone will figure they can profit by gaming this system and writing posts which appear to be someone else. All they have to do is try to clone an author's style and then feed their attempts to the analysis program to see how close they came. Then they can just fine-tune things until it's a strong enough match and push it out there as legitimate.

Yep, we might just have a "linguistic similarity analysis arms race" at some point. I concluded this in a post some months back. http://rachelbythebay.com/w/2012/08/29/info/