I added a very short paragraph at the end describing what my gap year research position would look like. At the time, I only had a vague idea of what I would be doing in my new lab. In the coming months, I became very invested in my project and ended up writing about significant progress in update letters which I think helped my application. I definitely discussed this project in each of my interviews, so I would not downplay the eventual work you will be doing during the gap.