This comes from the "Just some suggestions" thread, which i am going to split up.

New Gamemode:
Smth like assault would be nice. One team holds the entire map, but cannot build anything the other teams has just a small base and needs to take the whole base.
For balancing issues you should disable siege cannons, or limit them and take care for that the defending team doesnt rush the attacking team. Rines could have BIG sentrys in their base or maybe a laser-fence and aliens might have some kind of killer goo that just kills rines on contact.

sounds like the funny siege maps

Depending on the maps size, give the map a time limit of 30minutes-1 hour. And make it so the defending team can't enter the attacking teams base untill 3/4ths of the way through the game.