Make a vehicle usable by multiple players at the same time (eg driver and gunner).
What ?
It would be cool if vehicles can be operated by several players at the same time. Functions could be managed via "player roles". I can imagine the car to offer two roles: driver and gunner. The tank maybe can offer even more roles: driver, gunner, cannon operator, flamethrower operator.
The ability to steer, accelerate and decelerate would be attached to the driver role. The ability to operate the machine gun would be attached to the gunner role. etc ...
Important to multiple player vehicles are the following things:
1. Role management while on the vehicle
2. A indicator for which player fills which role(s).
ad 1. Role management while on the vehicle.
A player who is on a vehicle can cycle through the roles by pressing a cycle key, which is active while on a vehicle.
For the selection of roles I picture a very nice and intuitive system, where a player, entering a vehicle, locks into primary and secondary roles. Primary roles can not be taken by other players afterwards. Secondary roles can be taken by other players, if they select them as their primary role ore one of their primary roles. All roles not locked by a player remain open to be handled by all players on the vehicle jointly (which, I admit, can cause confusion) or not at all.
Example A
Player1 enters the tank and locks into the role of the cannon operator as her primary, and driver and machine gunner as her secondary roles, signalling she is up to do some heavy combat, but would be happy if another player joins her on the tank and does the driving and does the handling of enemies getting too close by operating the machine gun and the flame thrower. Player2 then hops on the tank, sees that, locks into the role of the driver as his primary (overriding her secondary) and the flame thrower as his secondary, signalling that he will play the chauffeur and handle enemies which got really too close. Player3 then joins the tank crew and locks into the role of machine gunner as his primary overriding Player1's other secondary. And off they go to the nearest hive playing monster of war, bumping into spawners, shooting far range shells, spitting bullets and roasting everything that is unfortunate enough to be too close. While in combat, on some occasions, Player1, who is a one woman army, hops out of the tank, to shoot a nuke at some distant part of the hive. While which the role of the cannon operator becomes vacant. But no problem. Player2 sees this and selects the cannon as his weapon and shoots some shells, while she is outside, without locking into the role of the cannon operator. When Player1 hops back on the tank, she is automatically assigned the role of cannon operator, because the game engine remembered which were her last primary and secondary role assignments on this vehicle and automatically assigns them to her, whenever she enters this particular vehicle, as long as they are not locked as the primaries or secondaries of another player. Secondaries override vacants and primaries override secondaries. At some stage Player4 comes out to the battle zone with a second tank all by his own. Player3 sees that and decides to help out in the second tank. When he leaves the first tank, the game engine again remembers that the role of the machine gunner was Player1's secondary before Player3 joined the tank crew and automatically reassigns it back to Player1 as her secondary. Unfortunately the second tank gets torn apart by the enemy because Player4 is a bit inexperienced and didn't see that it is not a good idea to lock into driver, machine gunner and cannon operator all as his primaries, leaving just the flame thrower to be fillable by Player3. Player4 also dies in this mishap. Player3 makes it back to the first tank and automatically gets assigned the role of machine gunner by the game engine.
I believe you get the idea.
Example B
PlayerX is a newbie and does not know the joys of team vehicle operation. So he enters the tank and locks into all roles as his primaries, effectively locking this tank against other players. When he enters combat, he wonders why he is much less efficient and much more stressed out, compared to the other tank team.
ad 2. An indicator, which player fills which role(s). This could be done via a list in one of the screen corners which is displayed once in a vehicle. Stating something like (for the example of a tank with four roles)
(D) p Player2
(MG) p Player3
(C) p Player1
(F) s Player2
Primary and secondary roles can be indicated via nuances of a players color and additionally by a "p" and a "s", just in case some players colors are the same or close.
Even more ideas ...
There is a lot more to roles on a vehicle when starting to brainstorm about it.
The simple passenger role
A role that just allows to sit on a vehicle. Sit and be transported. Passenger wagons anyone?
The able passenger role
A role where a player sits on a vehicle and can stick out and use her/his own weapons. Anyone up for a party biter hunting train, a transport helicopter, a seat on the buggy, which allows not only the use of the buggies machine gun for drive by shooting (in this role the buggies machine gun would get added to the players own arsenal for the time in the role), but also the own rocket launcher for drive by nuking?
Mutually exclusive roles
Picture a helicopter with these roles: 1 pilot, 1 machine gunner, 10 able passengers. All mutually exclusive, because the pilot and the machine gunner can not be also 10 passengers. Or making it mandatory to have a 2nd player as gunner on the tank/buggy to make it useful in combat?
These are all wild first thoughts on the possibilities. If this feature will be considered to be implemented, I hope it to be given thorough thoughts on the moddability. It would open so many possibilities with, I believe, little effort. Should I write an additional mod api feature request as a complement to this feature request?
Why ?
Multiple player vehicles, in whichever game they were implemented, always added a lot of fun to multiplayer gaming. Also they added a nice bit of a feeling of team effort when jointly operating a vehicle.