It would be nothing special. It would take the communication aspect from this mod and give it to zombie and headcrab NPCs. A headcrab seeing you would cause a nearby horde of zombies or swarm of headcrabs to converge in on your position. Settings like "headcrab spawns near zombie every five to thirty minutes" or so. Patroling? Stalking? Headcrab burrowing? Ability to break down doors? Some stuff that generally improves the performance of zombies or headcrabs in game and makes them something more than fodder.
I was just thinking that it would help provide urgency to Zombie maps, maybe add some pressure to the player to promote tactics. Meh.

Perhaps some other aspects of this mod. I lack the skills/resources to do it myself, so I'm just tossing the idea around. That, or I'm being stupid with this.
(Correct me if I am being stupid. It won't hurt my feelings)