I really hope for the enemy AI to have line of sight. One of the few things I always have a small problem with in Rockstar's open world games is the complete lack of stealth unless it's a forced situation. I'm not looking for a stealth game, but I just want more realism in the way enemies react to you.
"Open-world" shouldn't just be the environment's layout. It should also be in the way you choose to complete missions, because when you allow players to come at a situation from every angle, the AI should react accordingly. Simply put, it just doesn't make sense for enemies to know exactly where you are at all times once you are in a certain area. They should be as smart as possible, but knowing the player's location should be based on their vision and hearing.