The mode would basically be the regular game mode where a predator hunts the fireteam and the team tries to complete their mission but the addition is 2 extra players that volunteer to lead the AI defense.
These two players would have missions that are opposite of the fireteam but coincide with the fireteams objective locations.
An example of their first objective could be these two on patrol spotted an enemy helicopter and they need to make it to the outpost that is under attack get by the fireteam and trigger reinforcements then fight along side the AI to defend the camp.
Then moving forward with more similar missions that involve getting info about the fireteam to the next objective to call in AI reinforcements and help fight off the fireteam.
This 2 man team could be somewhat weaker than the fireteam but have more chances to respawn/reinforce and attack the fireteam and/or predator.
This mode could have a longer game time and maybe one extra reinforce for the fireteam as compensation for the added difficulty of real players fighting along with the AI /calling AI reinforcements in on them.
So its a 1v2v4 game mode that allows for a lot of emergent gameplay as players potentially get in 3 way fights between fireteam defense team and predator.