Although this is probably impossible - id love the game to be just organic... OK it may need missions in there to add some spice and continuity, but id just love to be a boss (or grunt and work your way up) of a gang... whilst the world around you had other living and breathing gangs, taking territory, businesses at random depending on their strength, relationships etc.
So in theory the game never ends.... you are always trying to take more business, maybe you are big in exporting dodgy cars, but then you get a slice of the drugs business and are in a war with some Cubans. You lose the war and credability, but hang on and re grow your gang etc
This way the game goes in many ways, recruiting people, executions, drive bys - not just as set pieces but a real part of the game and a real part of stategy.. kill the wrong person and start a war, or setup alliances etc to control more of the city.
Its hard to explain, but thats how id like it to play out. Think of all the crimes that can be done.... having cops that have their own AI, maybe you can bribe some, maybe you get busted and have an insider to cover up your illegal doings.