I'd just like more modifiers in general.
Stuff like:
Triple burn: all burns are active
Speed: Movement speed (normal/ads) is (greatly) increased (guardians and enemies)
Explosion: all enemies explode on death (cursed thrall or firefly explosion)
Grenadier2: grenade radius is doubled
Move or die: Guardians take damage while standing still
Fast finish: the faster you finish the NF the better the rewards (e.g. guaranteed exotic if you are fast)
Chaos: 2 different enemy factions spawn in each encounter (this may be hard to do)
I don't know, just some fun modifiers, that maybe change the game a little bit, doesn't matter if it makes it a lot harder or easier, it just has to be fun... You know, instead of constantly using grounded and trickle, that's just boring.
I realize not all of these may be good ideas, but this literally took me less than 10 minutes to come up with, so I'm sure bungie could come up with some great stuff if they tried.