I think it would be possible to code an exact copy of the BF2 commo spotting system in ArmA. You'd point at the terrain, hit a button and it'd bring up a menu, you'd select an icon and the icon would go onto the map where you were looking. If the map marker was close to a known enemy unit the marker could follow the enemy unit around on the map, disappearing after some time. The code practically writes itself.
And to speak of "the BF2 squad system" and how ArmA doesn't have it... you have to enumerate the features of the BF2 squad system. What exactly are you looking for?
1. Give orders to group members. Check.
2. Add squad members to your group on the fly. Check.
3. Respawn group members on squad leader. Check.
4. Mark map for other squad members. Check.
5. Dedicated voice and text channels for squad. Check.
ArmA has all this. What does BF2 have that ArmA doesn't?