Coop 100% Idea

Im using 4 player GTAVC here as an example, but III seems also good for this.

There's 4 people and they all will start GTAVC at the same time. Nothing fancy yet, but the catch: Their games are linked together via some tool that reads and edits memory addresses.

If one player picks up a package, it will count as picked up for all players: Each player's package count will go up, the respective package will disappear for everyone (since it has been picked up), and each player gets to benefit from the rewards (weapons at safehouse, % increase etc). Same goes for Rampages, USJ and Robberies.

If one player purchases a safehouse, that safehouse will unlock for all players: The purchase token disappears, a save icon appears, and % increases.

Same for missions & phonecalls: If player 1 finishes BAB, then the BAB marker disappears for everyone and will start triggering Jury Fury instead.

Taxi fares: Each time a player finishes a taxi fare, counter increases for everyone. 4 players could be doing 25 fares at the same time and taxi driver would pass since 100 fares have been done. paramedic/vigilante behave more like missions though, so one player would still need to do 12 levels (have fun arguing about who will do paramedic, although once one player has done it, everyone will gain infinite sprint)

SSA cars would be marked as delivered for everyone as well once one person delivers one.

Other factors, such as time/weather and other non-progress related stuff, could still be separate.

Issues:
Money: Who gets money? If one player collects a package, should just that player get $100, or all players? Or should the $100 be split evenly across players (everyone gets $25) Or maybe the money counter should just be syncrhonized across all players.

Mission PBs: If one player gets a 6 second cone crazy time, should this apply to everyone and lock them out of gaining $? Or should it remain a PB and merely give % to other players and not update their best time?

Passing a mission while someone is doing it: If player 1 completes BAB, but player 2 is halfway through, what should happen? Should it abort the mission? Should it do nothing when he finishes?

Lag: Kinda the same as the above, but what if two players pass BAB at the exact same time?

Programming the tool: There's a LOT of variables that track progress. Each mission & phonecall has its own "have_i_been_completed?". Certain missions also trigger a lot of stuff to happen: Activate certain car spawners, Remove bridge barriers, make traffic use these bridges again, remove cortez's yacht, start new threads to unlock the next mission, mark the starting cutscene as watched, play radio broadcasts, and even change the weather pattern. All these consequences would probably have to be stripped from the main scm mission code, and be called using the memory value program instead (so they can be done on everyone's end while they're doing other missions, and also to avoid them happening twice in case earlier mentioned problem occurs where two people do the same mission.)

Game crashes: The tool might cause game crashes? But on the other hand, if a player does crash, the tool could restore progress when they tune back in without a need for a save.

Grand scale: Is this too ambitious, even without the stuff mentioned below?

Cool ideas (optional):
-Garage cars are transferred. Player 1 puts a tank in the garage? Player 2 can get it out.
-A sort of ghost object put at the location of other players
-Inform other people of what just happened. Display a package counter when someone else picks up a package, including the beep sound made. Play mission passed music & show money earned if someone else passes a mission. This could even extend to SSA car cutscenes, if we want to be annoying


In short: This idea is already very similar to a coop multiplayer game, although no information like bullet trajectories, real time player positioning data, enemy status synchronization, etc is needed. (dammit MTA, why couldnt you just do this?) It'll still allow for very interesting routing. (what do the other players do while player 1 is doing The Party?)