well, we have the monstergroup field already. Maybe another ai extension, like self.groupevent, which could be triggered by a group leader, or the first group member to spot the player acts as group leader.

Quite possible.

I've been thinking about certain AI related map entities for a while as well, like info_ai, info_cover, info_shore etc.

Somebody's just got to sit down and actually code the stuff. :-E

Then again, they shouldn't become too smart. 

Hyper intelligence isn't a game breaker - even if the Ogre can beat you at chess, you can still shoot him in the face.

In other words, if the 'intelligence' doesn't changes to their actual abilities - like x4 movement speed, reloading or double health, then all it will do is make the experience deeper, as opposed to more difficult. 

I actually quite liked the contrast of the marine enemies in Quake 4 against the standard dumb monsters. Was a cool bit of variety, and allowed combat styles to mix up a bit. I wouldn't want most of the game to be like that, after all it's a old style shooter.

I guess basically enemies that have some kind of survival instinct is the basic thing. They take cover, can get injured and try to run like HL marines (no high bar for you their at all) :p 

True, the orange Strogg marines with all their different gear and their little hiding tactics were my favourite enemies in Q4.

Not sure if they acted as groups. I remember them talking to each other during combat, though.