Edit: I initially posted this as part of a larger feature request. I've since realized this was due to my lack of familiarity with Notion. It already works as I want it to. It's just more sensitive than I was aware for rest placement. I am moving the other features to their own request (as they are very different anyway).
Rest Insert Mode (Displace vs Replace)
When I place a quarter rest on an 8th rest, I want Notion to update / replace the rest, not add extra rests to the measure. Think of it like the "INSERT" key on your keyboard. One mode shoves **** to the side and one replaces. Wouldn't this be freaking cool in Notion? I think so! I also suggest making the keyboard shortcut for this, the "insert" key. ;)