I actually like this idea. I used to play the Battlefront 2 campaign missions so I can see how long I live against the infinite spawn of enemies.
It should be set up kinda like this:
-Only you and a group of reinforcements
-When the reinforcements die, they can't come back until about 5 minutes or so of survival
-About 5 lives, but can add up after a long time(like 20 minutes of survival without dying.)
-One spawn thats against a wall
-Some cover for reloading, low health
-Keep Health/ammo droids, make them very destructable and in wide open so they can be destroyed
-Increased amounts of enemies as time goes
-NO ROUNDS, but time of survival
-Constant enemy reinforcements while growing in numbers as time goes
-Co-op mode(off-course!

)
-Enemy ships come down to drop off enemy tanks and speeders
-It should be Clones fending off droids, or rebels holding off stormtroopers
-No hero bonuses, but heroes can come in from the attackers
Thoughts?