Grand Theft Auto 6 has not been officially announced yet but a patent that Rockstar Games filed regarding the AI. After some digging, it appears that it will allow for better performance and improvements such as the removal of disappearing cars.
GTA games always have one thing in common - the cities are populated with NPCs, some of whom drive cars, and if you take a look in the direction opposite of a car, it can disappear. The reason this happens is that the devs are trying to keep your rig viable for running GTA games by reducing the toll having so many vehicles and NPCs around would have on your performance.
One Redditor broke down the specifics of a recent patent filed by Rockstar Games, which pertains to AI. Some lines here obviously reference the issue mentioned above and if the new AI gets implemented, GTA 6 might finally get rid of the disappearing car issue as NPCs will still be in your game, even if it's not rendering them.
This is not all, however, as the AI will be able to navigate their vehicles better in alternative conditions. These can include bad weather, traffic and even high-speed chases.
Furthermore, the NPCs will be able to react better to the oncoming traffic, which should hopefully lead to fewer erratic movements where the NPCs drive their vehicle straight into the player's instead of avoiding the car crash.
All that said, this is still in the patent phase so it's not guaranteed that all of these technologies will be implemented in the final game but the indications are certainly uplifting.