I'd like to see a game where vehicles/equipment are constructed and maintained by the players in a multiplayer environment.
Having (not necessarily realistic) physics decide the functioning of your stuff rather than relying on numerical stats. I honestly think it's possible on a limited scale today (not on MY computer, but on higher end ones) to do something like this. Combat in such a game would probably be slow and "clunky", but would have a lot of strategic depth. The equipment and procedures you use would be more important than the twitch skills of the players.
A pipe, a slide-out joint along it's length attaching it to a metal block with a spring-loaded pin ending with a knob going through the block. A latch attaches the pipe and block. Six preprogrammed items. Designate grip points on the pipe and knob, push and pull actions for the pipe relative to the block, a toggle for the latch, a 'load zone' in the back of the pipe, and a pull and release action for the knob. You now have a primitive breech-loading cannon or shotgun. Throw some tags on it so player's scripts know what it is.
Now, you could either Receiver it out with radial menus/keyboard shortcuts, or macro them. A simple 'shotgun' script for it could be:
Change grip mode to normal. (You hold the item in front of you aimlessly, and let the computer take care of where you place your hands)
Toggle latch. (Action implied by primitive)
Pull pipe-block. (Action specified by item maker)
Take "Load". (Grabs anything in the zone 'Load' and puts it in your inventory.)
Item "20x70mmLow" in zone 'Load'. (Takes the first item with the tag "20x70mmLow" in your inventory, and attempts to cram it in the predefined zone. You did make sure to tag compatible ammo, and ONLY compatible ammo, right?)
Push pipe-block. (Action specified by item maker)
Toggle latch. (Action implied by primitive)
Change grip mode to point. (Holding item with it's "front end" pointed in your aim direction with your hands on the points specified by the item maker)
Wait for left click.
Pull-release knob. (Action specified by item maker, possible because a hand is on the knob and the other is holding the pipe)
Wait 1/8th of a second.
Repeat this script.
Looks complicated, but it's just 11 simple instructions.
The character should hold the gun out, unlock and open it (precalculated animations done at crafting time), put whatever's in it into inventory (displaying a warning if there is nothing to get), put a shell from inventory into it, close and lock it, point it forward like a weapon, and then wait for the player to click. When the player clicks, the character should execute one last action which starts the only part with heavy realtime physics simulation.
The item that was loaded is hopefully some kind of explosive. The pin in the gun intersects the item with significant force, causing the item to be 'woken up'. A check is run for any effects of a sharp impact from the back. If there is none, the item is put back into sleep mode. If it's a shotgun shell, obviously, a large portion of it explodes. This occurs in a pipe with one closed side, so, assuming the pipe and end blockage have the strength to survive it, instead of spawning a proportional explosion object, the parts of the item in front of the explosion are moved to the end of the pipe and given velocity proportional to the pressure and pipe length. These components are now projectiles, with all the physics simulation that entails.
Then the script restarts itself.
For the end user, the makeshift shotgun is simply an item with an ammo type and a script. While the script is running, the character loads the gun and fires it at whatever is clicked, returning any remnants of the shells to the inventory manually.
I could spend all day making items in a game like that...