Of course, there are probably some short cuts but these would require some interesting thinking on the implementation side.
First one I could think of would be the 'herd'. We've all (well most of us) have seen nature programs showing the grazing animals reacting as a single entity / herd due to an outside influence.
Implementing a system where attacking one makes other members of the same mob react in an appropriate manner. However a player attacking one atrox and the other 10-20 atrox in the area all attacking wouldn't make MA popular with that hunter.
Equally a stampede of exo running through the servers because one noob shot a young wouldn't be good.
This is ignoring that old story of where one animal gets attacked, killed and eaten while other members of the same species stand around and just carry on as normal (i.e. like now in EU) afterall what have they got to worry about the predator has something to eat.
There's also the parent animal protecting its young from an attacker so an older more mature mob would attempt to protect a younger from being attacked. In this case attacking a young would make the mature attack.
The second approach would require the least effort as it just means the mob agro code would need an extra input from surrounding mobs attack state.
Both methods could result in a single player being overwelmed just because they attacked a single mob. The second idea would require the least processing power on client and server sides.
The other behaviour we usually assume with enhanced ai would be if mobs could dodge and weave to avoid being shot. I don't believe this would work with EU because of the cheats MA put in place to reduce lag and rubber banding. We get rubber banding as our clients tell the servers where we are at fixed intervals, we've all experienced it at some time and it also affects mobs. So what happens when a mob dodges to avoid a shot.
The same or very similar code used to estimate our position during those intervals is used to work out where a mob is. Often the best way to hit a mob thats moving in parallel to our own position (i.e. its running at or away from someone else) is to shoot slightly in front to allow for the lag between the shot and its movement. For a hit to count, where the mob is and if our shot passes through the same location has to happen at roughly the same time, this partly handed by the server and by the client.
Adding an ability to dodge a shot is too demanding as it means the time intervals between working out the mobs location and our own would need to be much smaller and could result in even more lag due to higher network traffic.
For example, a mob has triggered its dodge and on our client we've shot but it's counted as a miss as the server has the mob in a different loction even though we've shot right at it because the time for the servers to tell us where the mob is is too great for our systems to cope with. Remember that all the clients / players have to be told a mob has dodged for people with a large ping time to the EU servers it could mean seriously bad game play and no two members in a hunting party having the mob in same position unless they're in the same room.
The current system estimates this out by calculating the location and handing some of the processing to the client. Everyone is working at the same time and using the same calculation so a mob appears at roughly the same place for everyone in the area.
Even if the mob dodging was implemented client side the other players in the area would get lag as the data would need to be send to and processed by the servers, then sent to the other players. Every client would be fighting each other for dominance unless your going to limit it to the player it's currently attacking.
The position time interval was calibrated by MA a few years ago in VU8 (I think) when physx support was added, almost everyone experienced rubber banding and it gradually reduced as they got closer to the best timing. Before then jumping off a mountain was a 5 minute wait to hit the bottom as the system fought as it new no one could move that fast
This timing can still be screwed up if people start a big download while playing EU.
MA use a chase algorithm for an agro'd mob which is simple, an example is at the link below.
Building Brains into Your Games
