You could do some sort of control points mode, 3 or 5 points scattered across the map you must take and hold, gaining, say, 1 point for your team every 5 seconds you hold one, and the first to 200 or 300 points or whatever, really, wins.
Also, an attrition gamemode: you get a select number of attrition points, and you have to destroy the enemy with the points you are given, but here's the twist. Whatever you use costs a certain amount of attrition points, so if you die then you lose these points, so a rifleman might cost just a few attrition points while a mammoth tank costs dozens so you must use what you have wisely.