I was at one of the Academic Integrity events that TII held in the UK in January; my understanding of what they were saying is that they're starting to look at that; both dramatic changes of writing style within an item, and between items submitted from the same student. There aren't the tools that can tell for sure, nothing is as good for that type of query about the authenticity as a human. I've always told both students and staff that TII isn't the only thing you should look at if you have concerns that the student didn't write all of the essay themselves. 

Of course, it is not a magic recipe to identify Frankenstein's works, it is really hard labor. However, the richness of that process is when teachers read and highlight all those words and phrases where there is a doubt because there is not good writing or vice-versa it is too much writing and emphasis in an idea from a student he/she recognizes in a learning process as a beginner, for example. So, students must edit and improve their work for the next review. Although it is not a specific tool from TI to contrast some specific phrases, neither to filter some references as Ithenticate does, always there are multiple options to feed and check student's papers.