Okay so this is the idea I had in mind when I first thought it up in that moment of inspiration.
2 dudes shooting each other from opposite ends of the arena, trying to dodge with their jetpacks.
However I did a quick test version this morning and it doesn't seem very fun, here is what I was thinking about between coming up with the idea and making that demo.
This is a more complex but probably more fun version. 4 guys in zero G. Use jetpacks to fly 'upwards', when not jetting the characters spin around, to be reangled and fly off somewhere else. Not sure whether to shoot while jetting (for lots of flanking attacks) or to do it whilst spinning around (which would make jetting just for evasion). As you can see I drew it with shooting whilst spinning.
The blue stuff is electricity. Touch it and die. Initially it was to keep the players from flying too high, but now I think it should another way for players to kill each other.
Shooting causes knockback, making all your flying around slightly wonky.
Getting shot adds motion in the appropriate direction, making it possible to shoot players into other things.
Players bounce off of walls and each other.
After taking more damage you recieve more force when shot? (kinda like Smash Bros)
Perhaps bullets will bounce off of walls once too (depends on balancing/performance issues)
If by some miracle I get this done rather swiftly, I'll see if I can work out online functionality. But the focus for me is a 4 players 1 keyboard type scenario.
Now to commence creation of new game!