Well I don't think this would be that a huge advantage to AI. I mean not that a big disadvantage for the human. IF AIs can threaten you in the game, they can threaten other AIs, isn't it? But if it reveals itself to be a real disavantage, the bonus should be bigger again!
Let me spell it out. This setup gives the AI the bonus with less of the penalty than the human player. No rule except the difficulty handicaps should do this, regardless of how major the effect. As for it not being a big disadvantage to the human player, let me put it this way; if you can beat a level higher than noble it is a major disadvantage. You can beat the AI because you are smarter than it, and you are effectively throwing away the effects of this by making the switch. The AI is losing nothing by making the switch, since the other part of the empire will be controlled just as well (or badly) as it would be in any case.
Well I don't think this would be that a huge advantage to AI. I mean not that a big disadvantage for the human. IF AIs can threaten you in the game, they can threaten other AIs, isn't it? But if it reveals itself to be a real disavantage, the bonus should be bigger again!
Any AI that understands how this works will always use it, so arguments about how the AI's interact will be fairly irrelevant.
The advantages should be exactly the same than the disadvantages, time included of course.
The disadvantages are almost entirely dependent on how good the human player is. The better they are, the more they lose by handing over control. If you scale the advantages acordingly the AI should get virtually no bonus as it has no real disadvantage.
I don't see a really good reason here. Plus I could argue that many people like me dislike micromanagement a lot.
Somehow I'd guessed you dislike micromanagement

. Fine, many people agree with you, so why not come up with a suggestion to reduce that? This suggestion is basically removing about half of the management (and not just micro) from the game. The basic point is that in a game like Civ I expect to play the game, not be encouraged to have the computer play parts of it for me. I generally try to be constructive with my criticisms, but this makes no more sense to me than having a big button which shuts my empire down for 50 turns, but makes one of the AI's spontaneously disappear. This falls into the same category as mods to completely automate your military. You're no longer really playing the game, and adding arbitrary bonuses to encourage you to do this doesn't change matters.
I've said my piece now, and I don't wish you to think I automatically rubbish all ideas.

It's just that this one really doesn't look good.