Yes the achievements are a good point to keep the game alive.Some achievement ideas from me:
SPECTATOR (AFK) achievements:
1. AFK monkey: Be a Spectator on server for 1 hour.
2. AFK banana: Be a Spectator on server for 5 hour.
3. AFK Monkey eats banana: Be a Spectator on server for 10 hour.
4.No banana for no monkey: Be a Spectator on server for 24 hour.
Bad Luck achievements:
1.Bad Luck: Pick up an enemy weapon that has not been reloaded or out of ammo.
2.Shoot out a full clip to 1 enemy soldier without hit him but he kills You with 1 single shot.
3.Be in a scope of an enemy sniper 50 times / 50 deaths- while in his zoom.
4.Fortuna is on Holiday! : Die 10 times without killing an enemy or destroying enemy vehicles.
:IS2:

Just some funny achievement ideas!