A lot of people want to the the return of private matches, rumble, and the addition of a ranking system in Crucible. I would like to see these things too, but I'd also like to see more fun and crazy things added as a new playlist of the Crucible.
It would be great to have a new playlist has added modifiers that rotate every week. These modifiers can increase jump height (gunfire should not cancel jump abilities), grenade regeneration speed, super regeneration speed, melee damage, etc.
EDIT: Modifiers for increased or decreased player health would also be nice.
The gametype of the playlist should also rotate, and once in a while, it should be Rumble (free-for-all) from Destiny 1.