For mini-less combat, I'm not sure how AoOs, OAs, etc., could be incorporated optionally.
I agree with the original poster that it is an odd nod to simulation in a tactical combat system that decided to make friendly fire from archers and magic users largely impossible.
I agree that there's more than one way to handle the situations that currently trigger an Attack of Opportunity.I see as the main reasons for attacks of opportunity: cost for disengaging and switching targets, interrupting spellcasters and preventing melee archery.
The first could be handled like charge: -2 AC for a round, maybe -4. The second would go away if all or most spells had 1 round casting time. For the last there's already a penalty for shooting into melee; if it's too small, just increase it further when you are in melee as well.