If you write a lot of narrative text in RStudio, you might find wordcountaddin useful for counting words and getting readability stats (in all or part of a document), and gramr for identifying bad writing styles.
We've already got spell check in RStudio, but I think it would be more useful and natural as lintr-style, on-the-fly spell-check built into RStudio, rather than hitting F7 periodically. Then we could get misspelled words underlined as we type, and listed in the RStudio Markers pane. That would really improve the writing experience in RStudio!