The main goal in minecraft is to have fun (or find diamonds :3) so you shoud add a diving suit.When you make a diving suit you whil need to find an ocean. So i thought you shoud add fish,wahles and even hostile mobs like sharks. and maybe even vilages under water. That last thing had no sence but here is the craftting for the suit.
i=iron l=leather x=nothing

l i l

l x l

l x l

that is only the helmet but thats the best i got.