here are some ideas of mine:
Impossible Scenarios (stolen from StarCraft):
Each player starts with different units. The goal is to defeat a nearby enemy base by working together. After you finish off one base, you get new units in a new area, with a new base to kill...ect.
Tag!:
One player is randomly chosen to be 'it'. The 'it' player is eden, the rest plymouth. Everyone starts with no buildings, and one scout. Then you, well, play tag. The last one tagged is the new 'it'. As each scout is tagged, it will explode! When the last person is tagged, the game starts over.
Freeze Tag:
The same as tag, but you are frozen when you are tagged. Other people can unfreeze you by tagging you back. When everyone has been frozen, the new 'it' is randomly chosen from the frozen people. Note: frozen people become light towers.
Shepard:
(Played on a very large, tall, hilly, rocky, ect, map.) One person is randomly chosen to the shepard (who is eden). He/she must get his/her sheep (scouts) from one end of the map to the other end. The other players (plymouth) must steal the sheep (by emping them and reprogramming them). Then they must take said sheep base to their base. Once in their base the sheep are exchanged for points (more info farther down). Shepards may build any unit they want to defend against the theives. Any sheep that make it to the bottom count as points for the shepard.
More on points and units... At the start of the round, your points are multiplied by 50, and added to 2000. This number becomes your ore for said round (both rare and common). Units are purchased as usual, but any war units (units other than base used units, spiders and emps) made by the theves will be destroyed. Or they could be disabled, but won't that stop the Shepard from making them?
Other things to consider... Mabe you have mines instead of ore budgets? Have the shepards only build scouts?