The linguistic focus is great, but here is an idea for later improvements. Those of us who practice expository writing often make sure we have good topic sentences (usually the first sentence in the paragraph). The idea is that if you just read the first sentences of each paragraph in a section, you would essentially have your synopsis for the section. If the sentences don’t do this, then this is a clue to revise your writing.
So, my humble request would be to have an option to apply linguistic focus to the first sentence of each paragraph.