This mod (or functionality like it built into I&A), would certainly add some chaos and uncertainty into I&A missions, and make them a bit harder, and/or less predictable.
Everything depends on how and if something can be implemented or not, however... I will agree, it would be nice to see this kind of functionality.
As I&A players, I think we are conditioned to not worry about the enemy until we get near the edge of the AO circle. That's actually not realistic, and we should be (forced) to be on our toes a little more on our way to the AO, and certainly around the outside of the AO. Landing just outside the actual AO, is usually quite safe, and again... it shouldn't be so.
Also, and I don't know how this would link in, we could do with some random AI spawning inside the AO during the mission, or patrolling into the AO, or at least patrolling around 'significantly' within the AO. The AI is just a bit too static and predictable, at times.
Whilst on that subject, and I appreciate server load and hence lag might be an issue here, how about spawning non-combatants, or neutrals, or even non-participating friendlies within the AO. Add a required element of SA to charging into an AO and just shooting at anything without a green tag on it.
You could add a friendly fire, or non-combatant kill tally to the score board, or strike off enemy kills for each friendly or non-combatant killed.
Rockfrog got a reaction from Bruce in INVADE & ANNEX AMBIENT ENEMY CONCEPT