Basically one day in the future this will happen. A new way to rank video game scores will happen. Of course it won't be the only way, but one day we'll have an A.I. score that ranks just how difficult it was for the A.I. to beat the game. The score will be simple. The ranking will be based on how many times the A.I. had to play the video game in order to beat your score. So if it took 10 times, your score is 10. If it took 5,000 times, your A.I. score will be 5,000.
Yes, there are problems with this ranking system. First off, some games are entirely dependent on chance for a decent high score. Ms. Pac-man is the perfect example of that, as getting a whole bunch of bananas in a row will increase your score dramatically. If the A.I. has some bad luck the A.I. score would be higher than a normal game.
Also, an A.I. would not think like a human, and so human difficulty of achievement would have some problems. Still, I can see an A.I. difficulty score being a measuring stick for video game scores.