"Hide Empty Staves" hides the left/right hand of the Piano if there's nothing there
Note: Even though "Reported version" says 3.5, this happened in 3.6. There's no option for it yet.
1. Take any score you have that has a piano in it and delete some of either the left or right hand. Make sure a whole system of either hand is empty.
2. In Format > Styles, check "Hide empty staves."
3. The empty part of the piano is gone. I don't know if that's how it's supposed to be, but that seems weird to me. I've never seen just one staff of piano, even if there's a stretch of silence in one hand.