If anyone has played the Pandora Tomorrow/Chaos Theory multiplayer, or the MGO gamemode (I can't think of it's name), you'll know what I'm going for with this.
The game mode would work where the Intruders have no lethal weapons, just gadgets like banana, smoke grenade, gas grenade, cam, etc. Whereas the Guards get all lethal weapons. The briefcase/hack objectives work fine because that's how Splinter Cell and MGO played out.
This forces the Intruder (spy) team to use a lot more communication and team/stealth tactics. I think it would add an interesting way to play whereas right now both teams are basically equal unless it's Mountainside.
Sub idea that could come with it:
Stun/tranquilizer gun for the spy team?