Zombie pathing is already cheap and runs off the main thread. I did fix a bug last week with only 1 path per frame being sent to the threading system and since it typically only takes 1 frame to make a path, it was a bottleneck for say 100 zeds making paths each second. A fairly simple change now has it requesting up to 8 paths per frame of which the threading system can provide about 6. This tested well with around 150 zeds on a server spread across 6 players.