This concept might prove some fun: A "steering" gamemode.
This would have you trying to steer or move something, like an train or a herd of cattle, by using some type of control. Like making a herd of cows run to a control point you just capped. You can't move the object backwards, just forwards.
So you'd make the object go form point A to point B.
But the real fun is getting them to the other teams base whilst defending the points the other team must cap to move their object. So the map would basically be split in half, with each team capturing points to move there deadly machine or whatever, whiling not allowing the other team to.
Any questions? I'll be glad to answer them
Its a bit strange, but could be fun for a joke map of sorts.