You may have heard of the Rule of Thirds, a rule of thumb for anyone who creates (moving) images. I try to utilize it as much as possible but sadly it's sometimes hard to judge in Minecraft where exactly a third of the screen is. So I'm suggesting that, whenever you press a certain key like
I, four lines get drawn, two horizontal and two vertical, at thirds of the screen:
At the intersections of the lines is where you should place the important objects in your video. As you can see, although I tried to put the boat on the bottom left intersection, because I added the lines in later so I couldn't see them while taking the screenshot, I placed it a bit too far to the right.
Such a feature does not sound hard to implement and it would definitely be useful to me at least.