Grenade bounce pathing. ie: you see how the grenade will bounce across walls ect. useful when playing maps you dont usually play, and making sure you are aiming in the right spot for tricky grenades.
Automatic smokes/flashes. ie, you hold down throw with a grenade in hand while standing in a certain location, a small indicator shows up on the screen for where to aim to get perfect long smokes/flashes. This one seems like it would be a ton of work, mainly from getting nade positions on each map, but would be a really unique feature that I dont think anyone has.