Where are these supposed billions?
Because populations are either already contracting or on the verge of contracting nearly everywhere: China, India, Nigeria, even Pakistan, etc.
The first things people do when they get richer is that they stop having so many kids.
it's a lame balancing act by the elites who based all their livelihood off masses of people to explore, and the need to be sensible with resources to keep the status quo a little longer.
china, when they were briefly communists, put a population limit as it was sensible when the plan was to make everyone enjoy the benefits of society. ...then they jumped to capitalism as usual and changed gears.
Anyway, there are no billions of new middle class people ready to buy a car there. You are far, far overestimating the growth potential and at the same time underestimating the current rate of vehicles ownership (mostly two wheeled).
Electrification, certainly, more A/C definitely, more cars, sure a bit but infrastructures are already under heavy load which limits the interest. Billions of cars, never.