In another wonderful RPG game I played, Dungeon Siege 2 (I love you forever) there was a system of "Anger". In DS2, enemies would usually swarm whatever was dealing the most damage, which was usually the extremely squishy sorcerers. To alleviate that, the tankiest class, the Shieldbearer warrior, had a power that would essentially force aggro around him/her. At the cost of taking more damage to the party (Angry monsters attack faster and dealt more damage) your damage dealers stayed alive.

This would be an interesting implementation, and would greatly add a depth of complexity to encounters.

yeah this is a pretty cool idea. players who run around just watching the battle will have to get involved now. it would also be cool if all monsters had 2 secondary attack patterns, cause the same attack pattern for every monster is getting old.

Ex: Trojans follow the status bombers and disregard the Blitzers (sometimes)
Through this, it shows that there seems to be 3 categories: hits, damage, closeness

Trojans could be blocking the haze status effect with the shield and continually accumulating points of "damage" that stack over time. These are hypothetical points of "damage" because there is no real damage being dealt, but the hazy stuff deals 0 damage which aggros them.
These 0 damage hits clearly cause aggro, which shows that #hits clearly is important, thus proving the 3 categories previously mentioned.

I'm got kinda lost in my explanation at some point ._. Hope someone understood it.

EDIT:
Ohhh yeah... +1