1.) Tagging The Enemy (Think Bad Company 2) - you press a button, and the person your aiming at lights up red on your team's map and screen, easy to implement, helps encourage teamplay.
2.) Constant Warfare (think MAG) - basically, the Resistance and Security are in a constant war. The background for Multiplayer would be a map of the Ark, and each faction would have "controlled areas". These areas wouldn't affect matches or maps, but it would give the community a reason for choosing their factions and possibly sticking with them longer. Maybe a good idea, not sure yet.
-> A better description of this is: The background screen for the MP is a map of the ark. Resistance is red, Security = blue. Lets say Security is winning, most of the map would be blue. Lets say resistance is winning, most of the map would be red. The way it would be counted would be: Every Tean games or so, whichever faction wins those games, they moce up maybe a centimeter (depending on how big the map is) or it could be like eveyr 100 matches, whichever team wins controls a whole section of territory. Or maybe even it could be like MAG with those little bars that increas every 5 victories for each faction, and when they get to the top the faction takes a whole area of the Ark.
I'll post some more of my ideas later, for now i think that's good.