Chozo: I use the dive to jump into a hiding spot. I also use it to jump out from cover since you can turn mid-jump; it's especially useful when you know someone is around the corner.
If I could dive shoot someone, that means I could jump from cover and, like John Woo, blast while in mid-air. That could be very useful when jumping from cover to cover.
If I could dive stab someone, it would be epic. Plain and simple. Diving then stabbing doesn't cut it. I've done it during zombies and there's a down period after you dive where you can't do anything (roughly a second).