Showerthought: groups of 1-3 tanks accompanied by squads of troops get helicoptered in to 1-2 random monuments and defend them for 15 minutes. After the 15 minutes heli's come to pick them up; the heli's can also be shot down (high health, quick extraction, good weapons).

Have it happen once at a random point in a 24hr real life day cycle so settling near monuments isn't overly OP. The AI would have to be pretty good or at least overwhelming in number (scaled to server pop) to force everyone to work together, at least at first..

Rockets and c4 damage tanks when hit in strategic areas, AI prioritizes targets with these in their inventory. Loot payout obviously needs to be high to make it worthwhile. I'm talking weapons and armor from troops, rockets and 1 M249 per tank, Maybe some kind of rare item to disincentivize large groups from camping players on their way to the action.

I think it would work because it would give the big groups something to work towards other than raiding, and small groups or solo players the thrill of some real action.

TLDR; TANKS