slingshots don't fit the game very well imo. besides, they would have a high reload time and low dmg against even leather armoured players. they would also have a short range and have a large spread, as they aren't precise.
now, *sighs* shields . . .
shields would be too complicated, and need to be HEAVILY limited. arrows MUST be able to pirece some, ones that can protect from arrows must slow down players. This make make the game far too complicted, and is likely a bad idea.