If Gran Turismo improve the AI to make it drive in a more believably "human" way.
I resumed your post in that sentence. I can´t talk too much but I am being part of a Closed Beta from a new upcoming racing game for PC (still in WIP phase, Work In Progress) and it is from SimBin and those who play SimBin games knows about how good is the AI and the sounds. (which in this game is going to blow your minds by the way)
But talking about the AI, they are implementing an interesting mode called "Adaptative AI" which is pretty cool I must say. It works in a simple way...you first practice or qualify and depending in your times the game itself makes calculations and puts an AI relative to those times. So by the time you drive and get better the AI gets better too.
And you can be amazed in how it works because it is like driving against yourself, and it feels like racing against real people at the same time as it happened in Race07 or GTR2 for example.
If you are the 1st and the AI driver gets a blue flag it let you pass inmediately, or you can get a blue flag if the AI comes from behind faster than you even in practice and it even makes you light signs, lol
It works pretty well and it is actually damn hard because as I said it is like driving against yourself and the AI at the same time uses different paths (not like a train in GT games) based in your own with its variants.
It is good for those who want a challenge and also for those that can´t set a proper AI difficult. (which is something that GT needs to put in the game not only PP system to decide which cars race against you...the level of the AI must be decided by you or the game like in B-Spec works for example)
So it will be great to see something like that...but in GT we don´t have qualify sessions before races which in a simulation game is needed for both SP and MP.
And what about having races online against both real people and IA´s to fill the places of the missing players in a race?