Making the traffic AI smarter and able to adapt to traffic as it's on route basicly means more calculations, which means more work for the CPU. If CO did that (which they have said they won't) it would pretty much mean people playing on computers at or just above minimum system requirements wouldn't be able to play (or at least only have tiny cities).
If your computer can handle it I'd recommend the mod Traffic Manager: President Edition. It has options for more advanced AI, better lane changing on highways and the lane connector to customize your intersections to handle traffic much better. However if your CPU isn't that powerful you'll notice the game will slow down with this mod (hence why we won't get the base AI changed that much).
It's also possible the new overtaking rules for emergency vehicles can lead to mods giving us smarter AIs, but again this will really be something for mods to do, since we can pick and choose them if our systems can handle it.
