Simple ideas:
-dropping ammo/nades/other items on death. It encourage working close to each other, because you can get some profit when your teammate dies near you.
-healing, but only other players (no self healing). that could include reviving
-bigger difference between weapons. If each weapon has it's specific purpose, hard to recreate with other weapons, you'd need more people in group to perform well. example: two weapons, one awesome at destroying cover, but weak at killing, and second good at killing, but harmless to blocks.
-classes (in form of loadouts, not set archetypes). I know a lot of players don't like it, but it's proven to increase importance of teamwork (W:ET as example). Even better if some of the classes are required to win but really fragile.
-weapons that require more players to operate effectively (for example HMG/mortar that require so much space that someone else need to carry ammo)
-giving more points on scoreboard for other activities other than killing, like tent capping, killing enemies close to your or their intel, placing blocks at your babel tower and destroying enemy tower (that is way easier to track than in CTI or TC
-just play TOW game mode - IMO it encourage teamwork the most of all available mods, because each team have only one object to attack and one to defend (like in CTI), but successful attack or defence require more players than one sneaky lone wolf tuneller (unlike CTI)
IMO squads are fine, but popping out of thin air around your teammates is just silly. I have nothing about para-dropping at marked location (risky and visible), or building temporary spawnpoints (visible to enemy on the map). Generally something that require some real effort to gain advantage of spawning anywhere on the map, not just hiding single soldier.