It should be obvious that this game isn't exactly best suited for PVP type endeavors because it just doesn't work well with GTA:O. Sure, one instance of a competitive game type works pretty well because it locks you into that separate realm that is the game session and you're on your way.
I'm the kind of guy that absolutely LOVED the SA Flight School update. I've always had the idea of giving GTAO a more MMO-like model for many things. Boss fights are one thing that i always thought would be interesting to see in GTAO. I always thought Rockstar could take ques from, say - the guy from the intro to Lethal Weapon 4 with the flamethrower and automatic weapon. Something along those lines. Seeing some guy armed to the teeth at the end of a mission in ballistic armor, taking you and your three GTAO friends to take him down - sometimes involving some strategy would be really neat.
I say, more PVE missions. More PVE in general. A lot of the competitive game types, IMO work fairly well in a Freemode instance. They're just far too contested at this point in one session and ultimately, it's an entirely different type of gameplay we're talking. The game is just far too biased towards PVP, by a noticeable margin.