The interesting thing about the Coreoline AU is that it actually follows canon fairly closely to the point where nothing about the overall gameplay really changes.
Like, in the 1st game within’ the AU you have have Cave guiding you through the test chambers instead. Hillariously enough, there are canon lines from the Perpetual Testing Initiative that kind of delve into what Cave would be like when poured into a computer. It even addresses how “living” for all of eternity and having vast capabilities can be boring enough to drive someone up the wall.
One big difference he has from GladOS? I don’t think he had to have his memories erased/stored away. So he could make reference to any manner of old Aperture elements and possibly brag even more since he had his hand in everything. I feel like he’d be decently talkative and very much like the pre-recorded messages in old Aperture in the 2nd game.
The kind of GladOS edge he has is akin to his bitterness he has in the 1970′s which he directs to his test subjects; very much treating them as being FAR lesser than him. Plus he’s a little bit eccentric due to his boredom and in truth, GladOS/Caroline has seemed to pick up things from him and perhaps even Cave in return because they used to work together.
All in all I think he would lack the kind of hidden resentment that GladOS has and would have other reasons for killing everything off and doing the things he did. If anything, Caroline is still the most tragic character compared to him since in this AU she still is forced to live forever as an AI.
So you do all the tests as normal and Cave chats on charismatically while still obviously doing his job (which is to test you) until he gets bored and starts to say some questionable things and you start disobeying him and escaping and all that. Then you have your final boss fight where he argues with you and tries to kill you since you’re a threat. Pretty much the same game, honestly but his personality and some of his dialogue is different.
