Just for prettiness purposes. Don't know if it's easily possible because of block states, but having the bottom-sloped versions go into the side of a chute that is open to the top kind of looks off, unless you're dropping something in there, too

No plans to implement this. Purely decorational, but would be a bit of a mess to detect when to use it. Adding even more conditional rendering is not on my list of things to do atm.