To begin with I checked the forums for something similar and I didn't find anything so feel free to post a link to a similar topic if I missed it.
Now, down to business. What if teams could call in airstrikes, tank convoys, or maybe just some helicopters?

Now this WOULD NOT be killstreaks since this game is more about working together to win than one's KD (in my opinion anyway). This "support" could be rewarded to teams for strategically working together or perhaps having a "comeback" in a match. For another way their could possibly be something like an airstrike called in from time to time from a certain point on the map like every 10 minutes or so. A similar example of this would be Battlefield 1943's airstrike bunkers which were usually situated in the middle of the map and any player could walk up to it and pilot some bombers as an airstrike and then there would be a cooldown. This would work well for a control point type of game mode though it would possibly not be very fair to the team who was losing especially depending on how powereful the airstrike (or tanks or air support) would be. On the other hand an ability could be given to both teams therefore making a little bit fairer. Also it would probably be easiet to give the fire support ability to the leader of the team.

Well those are my thoughts, so share yours.