So, control of units will always be under the domain of level 4, never any other level. The level above informs the level below, and otherwise they're totally separate. And in general terms with regard to programming, having multiple tools with specific purposes (Civ5 AI model) is much more effective and efficient than 1 tool that does everything (Civ4 AI model). So I'm optimistic.
It also seems to me that they're making the AI realize that they are playing a game, that they should try and win.
In every previous installment, the AI acts ideologically, or stupidly. What I mean is that they'll hate you just because you've chosen monarchy, and not for any tangible reason, really. Or they'll hate you for doing something that was simply wildly out of your comprehension that they would hate you for it. For instance, I once met up with france while coming up to the renessance era; just getting boats that can travel across the seas, and they immediately went to war with me because I had so effectively traded around with people he hated, and wasn't his religion. That's kind of stupid, both from a gameplay perspective, and also from any perspective that benefits him. He spent so much time and resources attacking me that the civs around him just basically absorbed him.
What I'm expecting to see is an AI that understands the tools it has, and understands the rules of the game. It will see that you have more iron then it, and see that it has a stronger offensive position currently, and calculate that it is a good idea to go to war with you, rather then just off-handedly deciding it should be so.
Also, the AI will certainly have goals, more then any other installment. The British will be naval, it would be stupid if they weren't. The Greeks will pamper to the City-States, it would be stupid not to. And we, the players, will know this about them, and be able to act in kind, just as the AI will act against us in a specific way depending on what Civilization we are.
If we're playing as the Aztecs, it would be STUPID of the AI to think we AREN'T going to war. A smart AI will simply ASSUME that the Aztecs, who get bonuses for killing non-barbarian units, WILL CERTAINLY go to war with them. A stupid AI will not, and will die quickly.
That's my largest hope for the franchise, is that all players, AI or otherwise, will always understand what the other players strengths and weaknesses are, and defend or attack as needed. It would be incredibly rediculous if the AI spawned as the Egyptians, and never attempted to build Wonders. It would ALSO be incredibly rediculous if the PLAYER spawned as the Egyptians and never attempted to build wonders, and the AI should know that. The AI should, and hopefully will, always be programmed to assume the other player is playing to his Civilization's strength.
If that can happen then we'll FINALLY be playing civilization as a GAME and not as a simulator.